A man who admitted to adding toxic substances to dumplings - poisoning at least nine customers in Japan and four in China - is likely to face at least 10 years in prison, prosecutors said on Tuesday.

Lyu Yueting, 39, admitted at trial at Shijiazhuang Intermediate People's Court that while working as a cook at Tianyang food plant in Hebei province, he injected methamidophos, a type of insecticide, five times in 2008 into frozen dumplings which were later sold to Japan and Chengde city, Hebei province in China.

The contaminated food made a five-year-old Japanese child "seriously ill" from food poisoning and other 12 people in China and Japan suffered minor illness, according to prosecutors.

The incident took place in January 2008 and sparked wide concerns over China's food safety before the Olympics.

Tianyang food plant was forced to shut down, products recalled, with a direct economic loss of at least 5.5 million yuan ($897,000). A total of 1,300 workers lost their jobs.

Prosecutors said Lyu's behavior caused serious consequences and he should be punished strictly.

Lyu, while admitting the crime, argued he injected the pesticides not to "intentionally harm others" but to "arouse the manager's attention and then take the chance to ask for a pay raise".

Lye had been working at Tianyang for 15 years, but he was still a "temporary employee" at the time when he committed the crime. He said the salary and welfare of a contracted worker at Tianyang differs a lot from a temporary worker.

"I was given 100 yuan as a Spring Festival bonus in 2007, while other contracted workers received thousands of yuan. I waited and waited. I thought I had work for the company for so long and deserve more incentives. I hoped the manager could pay attention to people like me," he said.

After having injected the toxic substances, Lyu said he wrote three anonymous report letters to notify the company's manager that the food has been contaminated, but the manager didn't take any action.