The Japanese government has decided to step up measures against highly venomous fire ants by designating them as an invasive alien species that requires urgent action.

Government officials made the decision amid a rise in cases nationwide involving fire ants. They fear the species, indigenous to South America, are on the brink of becoming established in Japan.

Experts have confirmed that more than 200 ants found at Aomi Pier on Tokyo Bay on Thursday are highly venomous fire ants.

The red imported fire ants were spotted at a container yard during a survey by Environment Ministry and other officials. The variety is native to South America.