At least eight people have died in flooding caused by record rainfall across broad areas east of Tokyo, Japan’s public broadcaster reported Friday. Heavy rain and severe storms struck Chiba Prefecture from Thursday through Friday. The Japan Meteorological Agency said Chiba City, the prefectural capital, recorded about 350 millimetres of rain in just 12 hours.

Chiba’s governor said at a Friday news conference that the rainfall was nearly three times the average precipitation for the entire month of August. It was the highest 12-hour rainfall recorded in the area since records began in 1976. From Thursday night until Friday morning, the weather agency issued its highest Level 5 heavy-rain warning for 22 municipalities in the prefecture.

The agency warned residents of unprecedented heavy rainfall and urged them to move quickly to safe locations. It was Japan’s first Level 5 warning since the warning system was revised earlier this year for greater clarity. Although the alert level was lowered Friday afternoon, rainfall was expected to continue. The downpour caused major disruption to electricity supplies and severely affected transport in several areas.