High moisture levels are causing atmospheric instability over the Kanto region centered around Tokyo and northeastern Japan's Tohoku region.
Weather officials are urging people in Fukushima, Chiba and Ibaraki prefectures to remain on high alert due to a heightened risk of rain-triggered landslides and overflowing rivers.
The Meteorological Agency says moist air from Tropical Depression Yun-yeung and the edge of a high pressure system in the Pacific are generating localized rain clouds over the Kanto and Tohoku regions.
Bands of well-developed rain clouds formed over Chiba, Ibaraki, and Fukushima prefectures on Friday.
Some cities in Chiba and Ibaraki got record-breaking rainfalls. More rain fell in a 12-hour period on Friday than the average for the whole month of September.
In Ibaraki Prefecture, Hitachi City officials say a road was blocked when a slope near a ramp to a major expressway gave way. Ten people were stranded in six cars and a bus. But police say they later managed to evacuate their vehicles on their own and were rescued.
In Chiba Prefecture, 11 municipalities reported first floor flooding, while landslides occurred at more than a hundred locations in 11 cities and towns. Officials have yet to determine the extent of damage in Mobara City, where extensive flooding occurred.
Landslide alerts have been issued in parts of Chiba, Ibaraki and Fukushima prefectures following heavy rains there.
The Meteorological Agency is asking people to stay on the alert for landslides, flooding in low-lying areas, swollen rivers, as well as strong gusts, storm surges, lightning strikes, and tornadoes.
Flooding and landslides have already been reported in the Kanto and southern Tohoku regions after record rainfalls.