Tokyo,  More torrential rain is expected to pound the coasts in Japan's north through Thursday, raising the risk of landslides and flooding, the weather agency said on Tuesday.

According to the Japan Meteorological Agency (JMA), warm, moist air from the Sea of Japan is adding to an already unstable low-pressure weather system, with the rain clouds forming likely to inundate areas in northern Tohoku and Hokkaido.

The JMA has asked people to remain alert for landslides, flooding and swollen rivers in the affected regions and said the weather front, along with torrential downpours, could also lead to lightning and tornadoes, reports Xinhua news agency.

The front is expected to move from northern to eastern Japan through Wednesday before heading toward the west on Thursday, the JMA said.

In areas in Hokkaido, around 6,500 residents from 3,600 homes were advised to evacuate on Tuesday morning, as the region has already been hit by heavy rain and is now bracing for further downpours.

The JMA said it expects 200 mm of rain to hit the Hokuriku region in the 24-hour period Wednesday, with Tohoku expected to see 180 mm of rainfall and Hokkaido 150 mm.

The Kinki, Chugoku and northern Kyushu regions, meanwhile, are forecast to see 120 mm of rain through Wednesday morning, the JMA said.

The weather agency also said a heatwave was continuing in eastern and western Japan on Tuesday, with the mercury soaring to 39 degrees Celsius in two cities north of Tokyo.