Tokyo, May 27 (IANS): Japan's weather agency warned of torrential downpours in some parts of the southwestern prefectures of Kagoshima and Miyazaki from Monday night through Tuesday, calling for caution as the rows of clouds may suddenly increase the risk of disasters.

The Japan Meteorological Agency (JMA) said on Monday that rain is becoming heavier, especially along the Pacific, due to a warm, moist air mass flowing into a front stretching from a low-pressure system hovering over the Sea of Japan, Xinhua news agency reported.

Very heavy rain and localised thunderstorms may hit, the JMA said, adding that linear rain bands could form in Miyazaki and Kagoshima in particular.

Rainfall in the 24 hours through Tuesday noon is expected to reach up to 300 mm in southern Kyushu, 200 mm in the Shikoku region, 180 mm in northern Kyushu and Amami, 150 mm in the regions of Kansai and Okinawa, and 120 mm in the Tokai region, according to the agency.

Weather officials said atmospheric conditions might get very unstable through Wednesday in areas from the southwestern regions of Okinawa and Amami to the country's east.

In the 24 hours through Wednesday noon, rainfall is expected to be 100 to 200 mm in the Tokai and Kanto-Koshin regions and 100 to 150 mm in Kansai and the Izu Island chain in the Pacific, south of Tokyo.

Meanwhile, the first typhoon of the season, Ewiniar, which formed on Sunday, is moving northeast while developing and is expected to approach the Daitojima region of Okinawa in southwestern Japan.