There is almost no chance the Chinese-made dumplings that made 10 people sick in Japan were intentionally contaminated during production, a senior quality official said yesterday.

"Reports that dissatisfied Chinese workers deliberately contaminated the dumplings are mere subjective guesswork," Wei Chuanzhong, deputy director of the General Administration of Quality Supervision, Inspection and Quarantine, told a press conference in Beijing.

On Tuesday, the Japanese wire service Kyodo said the food poisoning in Japan caused by the frozen dumplings was likely to have been committed by someone with a grudge against the management.

However, Wei said local police had confirmed with the administration early yesterday that they found nothing unusual in the production process.

He said sight inspections had found the Hebei province dumpling-maker Tianyang Food Plant was very well run and met high hygiene standards.

"It would be almost impossible for somebody to bring a poisonous substance into the factory," Wei said. "It's also almost impossible the contamination could happen during the production process."

Wei said the factory has been exporting to Japan for 10 years and its workers are very friendly toward the country. Salaries at the company are also much higher than the local average.

"The interests of the workers are closely tied to the Japanese importer, so there is no reason for them to sabotage the products," he said.

But Wei did not fully rule out the possibility that the contamination happened in China, as a police investigation is still ongoing.

He said the Ministry of Public Security had dispatched a six-member team, including top criminal investigation experts, to Hebei to study the case.

The incident has become an emotive issue in Japan following a series of health scares over Chinese products ranging from pet food to toys and toothpaste.

But tests have failed to find any pesticide residue in the dumpling samples. So far, traces of pesticide were found only in the 10 victims' vomit and packages of the dumplings they had eaten, but not in others from the same batches.

"Therefore, we consider it as an isolated case, not a food safety problem," Wei said.

Wei called for the establishment of a Sino-Japanese joint investigation team, as well as long-lasting cooperation mechanism on food safety issues between the two countries.