More than 350 people across Japan have fallen ill after eating pesticide-contaminated frozen food produced by the nation's largest seafood firm, national broadcaster NHK said Tuesday.

People have reported vomiting, diarrhoea and other symptoms of food poisoning after eating products including pizza and lasagne made by a subsidiary of Maruha Nichiro Holdings, according to surveys carried out by NHK and local media.

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.

NHK said that 359 people had become ill, while the Asahi Shimbun newspaper said it found the number of people who fell sick "exceeded 300".

Maruha Nichiro said that it had received about 460,000 phone calls from consumers in connection with the incident, including complaints from customers who ate the tainted products and some reporting an unusual odour, a company spokesman said.

According to local media, police suspect the pesticide was mixed into products at the plant in Gunma, north of Tokyo.

The food maker has recalled 6.4 million potentially tainted products, with 1.2 million packages recovered so far, it said.

Maruha Nichiro said that the products in question had not been shipped overseas.

The spokesman declined to comment on how the incident may affect the company's earnings, saying only: "We have to specify the cause first."

Separately, Japan's leading bread maker Pasco Shikishima Corp. was to recall about 445,000 packages of sweets after complaints that they had a strong chlorine smell, Jiji Press reported Tuesday.

A company spokesperson was not immediately available to confirm the report.

While incidents of food poisoning have occurred in Japan, including in August 2012 when cabbage contaminated with E. coli bacteria killed seven people and sickened dozens, food standards are relatively high.

However, the country's reputation for safe and high quality food suffered a body-blow from the after-effects of the Fukushima atomic disaster, in which acres of farmland were polluted by nuclear fall-out.