Venomous fire ants have been found in cargo taken to a warehouse in an inland city after it was unloaded at nearby Nagoya port in central Japan, the Aichi prefectural government said Monday.

The presence of the aggressive and invasive species, native to South America, was confirmed for the first time in Japan's inland area, said the Environment Ministry, suggesting that fire ants may have started spreading to wider areas of the country.

(Environment Ministry)

The prefectural government, together with the ministry's regional office, has searched the warehouse in Kasugai, Aichi Prefecture, and the cargo container that was shipped back to Nagoya port and found around a dozen fire ants. All ants were already exterminated and the cargo will be discarded, it said.

The owner of the cargo spotted a reddish brown ant with a blackish-red belly in the cargo at the warehouse, which is around 30 kilometers from Nagoya port, and notified the prefecture of the sighting.

The cargo container arrived at Nagoya port on June 30 and was taken to the warehouse on Thursday. It had been loaded at China's Nansha port in late June and shipped to Nagoya port from Hong Kong.

In a related development, insects suspected to be fire ants have been found in Nagaoka, Niigata Prefecture, on the Sea of Japan coast, the prefectural government said Monday, adding it asked a local division of the Environment Ministry for confirmation.

The ants were found in a cardboard box shipped from the Philippines which arrived on Thursday, according to the Nagaoka city government.

A sting by fire ants can cause anaphylaxis, a severe allergic reaction that can cause breathing problems and even death.

Fire ants have been found at several Japanese ports including Kobe and Tokyo.