In the busy streets of Hong Kong's Central district the lunchtime queues snake around the swanky Japanese restaurants where high-end sushi can sell at $150 a pop just for a tasting menu.

At Fumi, one of the more popular joints, the floors are packed with over a hundred people chattering away and chowing down.

"It's just as busy as ever," says Thomason Ng, Fumi's general manager. "Only a small portion of people have asked where the food is from. They're here for the dining experience and great hospitality alongside the food."

The great economies of Asia are clashing over the sea once again, but from the look of these customers either nobody told them, or they simply don't care.

The move by Japan, the world's third-largest economy, to release more than 1 million metric tons of treated radioactive waste water from the destroyed Fukushima nuclear plant into the sea has prompted a furious response from its neighbor and longtime rival China, the world's second-largest economy.

Soon after Japan began pumping the water into the ocean on Thursday, China announced that it would ban all seafood imports from its neighbor -- vastly extending earlier restrictions it had implemented on sea food imports from Fukushima prefecture in the wake of the plant's meltdown in 2011.

Hours before China's announcement, the Asian financial center of Hong Kong -- a semi-autonomous Chinese city -- imposed its own ban on aquatic product imports from 10 Japanese regions including Tokyo and Fukushima.

But while the well-heeled, international crowds populating Hong Kong's sushi joints may have largely shrugged off the local government's warnings, on the Chinese mainland the public's reaction has been rather less forgiving.

Calls for boycott

Chinese media -- traditional and social -- has exploded with anger at Japan's actions, with several state media outlets running critical editorials and opinion polls. A hashtag blasting the release gained more than 800 million views on the Chinese social media platform Weibo within just a few hours of Thursday's release.

China insists the ban is necessary "to prevent the risk of radioactive contamination of food" and has accused Japan of an "extremely selfish and irresponsible act that disregards the international public interest." It has repeatedly rejected Japan's claims that the water has been adequately treated and contains negligible amounts of radioactivity.

Many users on Chinese social media -- or at least the vocal ones -- appear to support their government's position, while many more have called on authorities to go a step further with a more wide-ranging boycott.

"We should ban all Japanese products," read one top comment on Weibo. "The Japanese are irresponsible," read another.

Experts say the strength of the response in part reflects the long history of animosity between the two Asian giants, which dates back to and beyond World War II and includes a variety of maritime territorial disputes.

Calls for boycotts of Japan are relatively frequent, breaking out whenever old grievances rear their heads or territorial disputes flare, they point out.

In 2012, trade relations sank to a low point when Japan nationalized a group of islands in the East China Sea claimed by both Tokyo and Beijing, fueling violent anti-Japanese protests across cities in China. The boycotts turned into violent attacks against Japanese-owned or branded factories in China as well as automakers and home appliance retailers.

Hitting where it hurts

That level of vitriol is not present this time round -- or at least not yet -- even if the ban appears designed to hit Japan where it hurts.

Despite their bitter histories, Japanese cuisine is hugely popular in many parts of China and business is booming.

There were 789,000 Japanese restaurants in China in 2022, with the sector valued at around $25 billion and growing. There are actually more Japanese restaurants in China now than there were before the outbreak of the coronavirus pandemic in 2019.

Those restaurants are likely to be hit hard by the ban, as are trade ties more generally.

Last year, Japan exported seafood worth about $942.4 million (137.7 billion yen) to China -- its top trading partner, while Hong Kong accounted for another approximately $432.3 million (63.2 billion yen), according to the Japanese government.

Then there is the Japanese fishing industry to think about, with local fisherman reeling from what they see as disastrous publicity.

The JF Fisherman's Cooperative Association, a nationwide body representing fishermen, has urged Tokyo to "take immediate action to address the reputational damage that has already been caused by rumors."

"Fishermen nationwide are feeling increasingly anxious at this very moment," said the group's chairman, Masanobu Sakamoto, following a meeting with the Japanese Prime Minister Fumio Kishida.

"We fishermen hold only one hope, namely that our fishing industry will continue to operate in peace," Sakamoto added.

'Not remotely harmful'

Critics have accused China and Hong Kong of hype and double standards, suggesting they are using the issue to score political points over a regional rival at the expense of scientific rigor.

The state-owned electricity firm Tokyo Electric Power Company (TEPCO) points out that in the years since the 2011 disaster the contaminated wastewater has been continually treated to filter out all the removable harmful elements and that it will be processed for a second time and highly diluted before being released over a period of decades.

The process will remove almost all radionuclides from the wastewater, apart from tritium -- a naturally occurring form of hydrogen that is the weakest of all of radioactive isotopes.

Many scientists back Tokyo's position that the water being released is safe.

In Fukushima, TEPCO says that some 7,800 cubic meters of water containing 1.1 trillion becquerels of tritium will be released in the initial 17-days of release.

That's equivalent to 0.003 grams of tritium -- the weight of about 10 strands of human hair -- said Nigel Marks, an expert on radioactive waste and an associate professor at Curtin University in Australia. By contrast, he says, there's currently about 8,400 grams of tritium already in the Pacific Ocean.

"It's not even remotely harmful," Marks said, adding that people are exposed to more radiation on an airplane flight.

"(Japan's release is) completely consistent with past practice all over the world. There's 60 years worth of scientific data of releasing tritium into waterways exactly like this and typically at far higher quantities, and nothing has ever happened."

Much more tritium has been released by normally operating nuclear power plants into the north Pacific Ocean from China, South Korea, and Taiwan, said David Krofcheck, a physics lecturer at the University of Auckland in New Zealand.

"Tritium is produced naturally as part of our normal environmental background radiation, and it travels via rain or rivers into the world's oceans. The water release is designed to have seven times less tritium per liter than is recommended for drinking water by the World Health Organization," Krofcheck said.

According to a study by the Japanese government, China's own Fuqing nuclear power plant discharged 52 trillion becquerels of tritium in 2020.

But these discussions are largely missing from China's state media coverage and on its heavily censored internet.

A number of articles trying to explain the science behind the discharge — including one from a Chinese nuclear expert who formerly worked at a government-linked institute — have been scrubbed after gaining traction on social media.

A drop in the economic ocean?

While some critics are accusing China of hyping the risks, there are others who wonder too if it has overestimated how much leverage it ultimately has over its neighbor.

While China is Japan's top seafood export market, it accounts for only 15-20% of Japan's food exports, and food exports account for only 1% of Japan's total exports, said Stefan Angrick, senior economist at Moody's Analytics.

"To put this into context, even in a 'worst case' scenario involving a Chinese ban on all food imports from Japan, the direct impact on Japanese GDP would be about 0.04%," Angrick added.

That's not to say Japan needn't be concerned. It is. Japanese Prime Minister Fumio Kishida has reportedly "strongly" requested via diplomatic channels that China "immediately overturn" the ban.

But Tokyo may be barking up the wrong tree if it thinks arguments about the science will sway China.

Fei Xue, a senior analyst covering Asia at the Economist Intelligence Unit (EIU), said the reactions of regional governments to Japan's actions have largely reflected the status of their diplomatic ties with Tokyo.

Still, Fei too thought that the bans from China and Hong Kong would have limited impact on Japanese trade.

"Seafood exports accounted for just 0.3% of Japan's total goods exports in 2022, among which shipments to mainland China and Hong Kong represented 35.8% of the total amount. Consequently, even considering the reputational damage for Japanese seafood products, Japan's overall exports will not be materially undermined," Fei said.

So long and thanks for all the fish

Back in Hong Kong, it remains hard to detect any lingering sense of either concern or outrage at Japan's actions.

Indeed, the release appears to have had very little effect whatsoever on the appetites of the crowds queueing round the restaurants in the Central district.

Part of the reason for this may be that chefs and restaurateurs saw the ban coming, with Hong Kong authorities hinting from the start of the year that it was on the horizon.

Many responded by widening their supply lines, sourcing their seafood from suppliers in Japan's Hokkaido, Kyushu and Kagoshima regions -- which are not covered by Hong Kong's ban -- as well as from Norway, Australia and Canada.

Because of that the menu at Fumi hasn't needed to change much, except for a little card letting diners know that the restaurant has followed the new import controls and sourced its ingredients from around the world.

At a shopping mall nearby, diner Cara Man, 33, was tucking into her lunch at sushi chain Senryo. She said that people still craved their favorite Japanese dishes, regardless of the news.

"People might start paying more attention to the radiation levels in their food if there are reports of people getting sick, but that isn't happening right now," she said.

"So we'll probably keep eating Japanese cuisine like nothing happened."