People have reported vomiting, diarrhea and other symptoms of food poisoning after eating products including pizza, lasagna, and croquettes made by a subsidiary of Maruha Nichiro Holdings, according to a survey by NHK.

Bloomberg News said the Tokyo-based food processor announced Dec. 29 that it was recalling 6.4 million packs of frozen foods, including pizzas and croquettes, made by a unit in Japan’s eastern Gunma prefecture. A statement on Maruha Nichiro's website said the company had completed 23 percent of the recall as of Jan. 6.

The Bloomberg article continued:

The concentration of the pesticide malathion detected in part of a croquette made by the unit was 2.6 million times higher than the permitted level, the Japan Times reported today, citing an unidentified Gunma prefecture official.

High concentration of the pesticide could be damaging to health if consumed in large amounts, Japan’s Health Ministry said in a statement dated Dec. 30.

Malathion wasn’t used in the company’s manufacturing process and may have been deliberately added to the foods after they were produced, according to the Japan Times report. Local police have questioned several workers responsible for the production line, the report said, citing an unidentified police spokesman.

Police began investigating the company last month after it revealed that some of its frozen food had been tainted with malathion, an agricultural chemical often used to kill aphids in corn and rice fields.