The storm cut power to more than 20,000 households and left 7,000 people stranded at Tokyo's Narita airport.
Japan's Meteorological Agency said the astir caller deluge was brought by warm, humid aerial flowing into the country's eastbound that combined with a cold aerial supra to marque atmospheric conditions highly unstable. The rains are expected to past done precocious connected Friday.
"This lawsuit was an highly antithetic situation, adjacent by Japan's humanities upwind standards," Chiba Governor Toshihito Kumagai told reporters connected Friday morning.
"I person responded to galore disasters successful the past, but I person ne'er experienced a lawsuit similar this."
Chiba, which sits close adjacent to Tokyo, has logged much than 100mm of rainfall per hr since Thursday afternoon, authorities say. This is astur 3 times the mean rainfall successful August, and the highest measurement of precipitation ever recorded successful the country.
Authorities would prioritise redeeming lives and persist with rescue efforts, Kumagai added.
At lest 8 radical person died, according to reports from nationalist broadcaster NHK, Kyodo quality bureau and Asahi newspaper.
Among those killed was a pistillate who died wrong her car submerged connected a flooded road, authorities said. Two others collapsed on the streets and aboriginal died.
The Japan Meteorological Agency earlier described the concern arsenic an "unprecedented level of dense rain".
Several obstruction services stay suspended connected Friday greeting portion immoderate large highways are besides shut.
More than 100,000 households person been asked to evacuate connected Thursday aft the rainfall triggered landslides and powerfulness outages.