TOKYO : Heavy rain that battered eastern Japan has left nine people dead, public broadcaster NHK said Sunday, after an "unprecedented" deluge that flooded over a thousand homes and snarled up roads and rail services.

Torrential downpours starting late Thursday triggered landslide warnings and power outages, with forecasters issuing the highest-level heavy rain warning for the Chiba region for the first time.

A weather station in the prefecture recorded 30 centimetres (nearly 12 inches) of rain in 24 hours, making it the area's wettest August in six decades.

By Friday morning, the city of Chiba logged more than three times the rainfall typically seen in the whole of August, Tokyo's land ministry said.

Nine have since died in the rains, NHK reported Sunday morning, citing its own tally.

Chiba's disaster management office as of Saturday evening listed eight dead, some trapped inside submerged cars and others found on flooded streets.

Over 70 houses across the Chiba region were partially destroyed by the rain, the prefecture's latest tally showed.

And over a thousand households reported being flooded, nearly 600 of which saw water surge above the floorboards.

An estimated 1,200 cars also remain abandoned on roads, local media said, with authorities working on towing them away or using jacks to move them.

An official from Japan's Meteorological Agency told a news conference on Thursday that it was "shaping up to be an unprecedented level of heavy rain".

Scientists say human-driven climate change is making extreme weather more frequent, prolonged and intense.