The Meteorological Agency will thoroughly investigate Monday's sudden wind torrent that blazed through Gunma Prefecture, blowing away roofs of houses and shattering windows.

Damage was reported in multiple cities, including Isesaki and Maebashi. In Isesaki, two people in a car were injured when it was overturned by powerful gusts, local authorities said.

Around 20 windows were broken by flying objects at an elderly care home in the city, they said.

"I was at home and looked out to find the outside almost white with falling hail," a 38-year-old woman in Isesaki said. "I also saw the door of a shed blown away and I was very afraid."

About 3,300 households in Isesaki and elsewhere were temporarily without electricity after the wind brought down a power line, Tokyo Electric Power Co. said.

Meteorological experts have not confirmed if a tornado occurred.

The Meteorological Agency said the severe weather was caused by two cold air masses — one of minus 9 degrees

and up to 5,500 meters high over the Kanto-Koshin region, and the other of minus 12 degrees above the Tohoku region — while temperatures at ground level topped 30 degrees in some locations.

The huge temperature difference made atmospheric conditions extremely unstable.