BEIJING - Restauranteur Xiao Zhang waited until late on Sunday night for her two guests to come back for a purse they had left in her care and pay their bill.

When her patience finally wore out, she opened the purse, only to find a note reading "The meal is on the Japanese."

The two diners, whom Xiao Zhang recalled as young women in their 20s, had left the purse with her, saying they needed to leave for an emergency and would return soon.

The women never came back. Their unpaid bill added up more than 1,000 yuan ($158).

This is just one of the anecdotes reported by Japanese restaurants in Beijing, many of which are under fire these days as agitated citizens stage anti-Japan protests and boycott Japanese goods in the wake of Japan's so-called "purchase" of the Diaoyu Islands last week.

Xiao Zhang, manager of a Chinese-run chain called "Daole Japanese Cuisine" who received a Xinhua interview using an alias, said she had told staff members to stop wearing Japanese kimonos.

The up-scale chain has outlets in downtown Beijing, including in the high-tech zones of Zhongguancun, known as China's Silicon Valley, and in a financial center near Xidan in the heart of the city.

"Business has dropped by more than a half since last week," according to Xiao Zhang. The Zhongguancun branch, normally crowded with diners from nearby office buildings on weekdays, was almost empty at 12 p.m. on Tuesday.

And that was not the manager's only concern.

"We have to stay low-key and alert," she said, referring to their uniform changes. Fearing harassment by protesters, staff kept watch at the entrance for agitated members of the public who might force their way in and destroy facilities.

The plight of Daole is common for the many Chinese dealers of Japanese products, whose businesses have been thrown into a state of uncertainty and tension amid ongoing anti-Japan protests.

Demonstrations were seen in dozens of Chinese cities over the weekend, with violence erupting in some places, resulting in a number of Japanese brand-name cars being destroyed and the looting of Japanese-invested businesses.

Appeals for boycotting Japanese goods are also gathering steam, bringing a lull to sales of Japanese cars, digital products, watches and cosmetics in China.

But bearing the brunt are Japanese-style restaurants. Despite their Japanese names and the Japanese dishes they serve, the absolute majority of these restaurants are run by Chinese.

Many restaurant owners claim they started up the business because they love Japanese food, which is increasingly popular among Chinese customers, too. Some of the restauranteurs have studied or worked in Japan.

Fearing sales slumps and vandalism by protesters, many restaurants have hung out Chinese national flags to avow their patriotic stances.

"Many customers are asking whether we are Japanese-invested, and staying only after we assure them of our Chinese origin," said a manager surnamed Wang at Japanese restaurant "Yizhi."

Like many others, Wang closed his restaurant on Tuesday, the 81st anniversary of the "September 18 Incident" that preceded Japan's invasion of northeast China in 1931.

In China, the date is marked annually with sirens mourning the war dead and rallies reminding the public never to forget history.

This year, the crowds of demonstrators are more agitated, a result of Japan's moves over the Diaoyu Islands.

Helu, a large sushi chain restaurant, had put up statements outside all its outlets in Beijing, claiming the company is "purely Chinese-owned with no links with Japan at all."

"All our employees are Chinese and our ingredients are from China," it read.

The head chef of Qianqin, a Japanese-style restaurant in Beijing, said he felt "sad and helpless."

"I love China and am furious at Japan's move, but I have a family to feed and there's nothing wrong in running a restaurant," he said. "I hope the storm will end peacefully soon."