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 has been reported in Gunma cities including Isezaki and Maebashi. In Isezaki, at least two people in a car were injured when it was turned by powerful gusts, local authorities said.
In addition, some 20 windows were broken by flying objects at an elderly care home in the city, they said.
Meteorological experts have not confirmed if a tornado occurred.
On Monday , the atmospheric condition was extremely unstable in the areas, with a cold air mass moving south over Gunma and setting off heavy downpours.