Weather officials are urging people across wide swaths of Japan to be on the alert for localized heavy rainfall, which could trigger mudslides and flooding.

The Japan Meteorological Agency says an influx of warm, moist air from the south is making atmospheric conditions extremely unstable.

Rain clouds passed over the Tokai region in central Japan overnight through Wednesday morning.

Radar analysis showed that about 100 millimeters of rain fell in an hour around midnight near the city of Nishio in Aichi Prefecture.

A gauge in Watarai town in Mie Prefecture recorded 89 millimeters of rain in an hour up to 1 a.m.

Weather officials say unstable conditions will continue on Wednesday from western to northern Japan.

They say Tokai and Kanto, which includes Tokyo, may see rain of up to 50 millimeters per hour, with a chance of lightning.

In the 24 hours through Thursday morning, rainfall may reach 120 millimeters in Tokai, and 100 millimeters in Kanto.

Weather officials are warning of mudslides, swollen rivers, and flooding of low-lying regions. They say lightning, tornadoes and hail are also possible.