More than 300 people across Japan have fallen ill after eating frozen food products contaminated with pesticide, reports said Tuesday.

Shoppers have reported vomiting, diarrhoea and other symptoms of food poisoning after eating food produced at a plant in Gunma, north of Tokyo, according to surveys carried out by the Asahi Shimbun and other local media.

The plant, run by a subsidiary of the nation's largest seafood firm Maruha Nichiro Holdings, is at the centre of the nation's latest food poisoning scandal.

Japanese police have launched an investigation into the company after it revealed last month that some of its frozen food products were tainted with malathion, an agricultural chemical often used to kill aphid in corn and rice fields.

According to local media, police suspect the pesticide was mixed into the products at the plant, which produced frozen foods including pizza and lasagna.

Asahi Shimbun said it found the number of people who fell sick "exceeded 300", while national broadcaster NHK said Monday that 359 people had been taken ill.

Maruha Nichiro said that it had received some 460,000 phone calls from consumers in connection with the incident, including complaints about sickening after eating the products, a company spokesman said.

Calls also included complaints about the unusual odour of some products and ways to return the products, the spokesman said.

The food maker had so far recovered some 1.2 million packages of potentially tainted products out of 6.4 million it wants to recall, he added.

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

The spokesman declined to comment on a possible impact of the incident on the company's earnings, only saying: "We have to specify the cause first."

While incidents of food poisoning have occurred in Japan, including in August 2012 when E. coli-contaminated cabbage 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.