Shanghai food watchdogs have reassured residents over the quality of local sushi after almost two-thirds of Japanese restaurants spot checked in Hangzhou failed bacteria tests.

The Hangzhou Industrial and Commercial Administrative Bureau said at the weekend that of 34 batches of sushi from five Japanese restaurants, about 65 percent contained excessive amounts of colibacillus, a bacteria that causes food poisoning.

Sushi from the popular Hangzhou Yuanlu Rotary Sushi Restaurant was found to have colibacillus seven times higher than legal limits.

After the results of the spot checks were released, consumer rights groups in the Zhejiang Province city warned elderly, pregnant and infirm people not to eat sushi.

Yesterday, Gu Zhenhua, director of food supervision department of the Shanghai Food and Drug Administration, said the city runs spot checks on sushi once a month. Ninety percent of sushi and sashimi tested in each restaurant must be within legal limits.

"Sushi is likely to be tainted during processing and go bad if it is held overnight," Gu said. "For sashimi, restaurants should have more awareness of temperature and timing. They are required to destroy unsold sashimi after four hours."

Shanghai Helu Rotary Sushi Co, a Japanese restaurant chain with branches all over the city, said its staff throw away unsold sushi and sashimi every day, according to an employee identified as Bi from the chain's operations department.

When the State Bureau of Quality and Technical Supervision said last week that some domestic ports had found imported seafood from Japan with excess amounts of metal, local Japanese restaurants said their produce came from local markets.