At least 10 people in Japan suffered pesticide poisoning last month after eating frozen dumplings - known as gyoza in Japan - which originated in a factory outside Beijing.
The dumplings were laced with a pesticide called methamidophos.
Thousands of other Japanese have complained of illness after eating dumplings from China.
The scare is the latest in a series of safety alerts to hit Chinese-made produce, with recalls in recent months hitting products such as toothpaste, car tyres and childr en's toys.
"The Japanese side says there is no possibility they were poisoned in Japan. We say there is very little possibility it occurred in China"
Public Security Bureau
With China's economy heavily-reliant on the export market, the government has been eager to be seen taking a tough line on safety in an effort to shore up consumer confidence.
The poisoned dumpling case has also threatened to strain improving bilateral ties ahead of an expected visit to Japan by Hu Jintao, the Chinese president.
The issue was further complicated last week when meat buns imported to Japan from China contained the same pesticide.
The Chinese findings run counter to claims from Japanese authorities that the contamination of the dumplings, produced by the Tianyang Food plant outside Beijing, likely occurred in China.
"The Japanese side says there is no possibility they were poisoned in Japan. We say there is very little possibility it occurred in China," Yu Xinmin, deputy head of criminal investigation with China's Public Security Bureau, told Thursday's press conference.
Wei added that the findings "do not exclude the possibility of a person from a third country or region illegally purchasing the relevant pesticide and bringing it into Japan," but offered no details.