Chiang Mai and Loei provinces took a pounding from storm Sinlaku as it moved into Thailand, with heavy rain and flash-flood warnings still in force until at least Tuesday.
The Kuang River overflowed its banks and flooded the municipality in San Sai district of Chiang Mai overnight. Residents escaped flash floods by moving to high ground.
Officials denied reports circulated on social media that the sudden flood was caused by a leak at Mae Kuang Dam in Doi Saket district. The flooding was due to damage to a small check-dam downstream in San Sai, built to slow the river's flow, officials said.
The Kuang River is a tributary of the Ping, one of the four main rivers in the northern region.
In Loei, torrential rain flooded communities in at least three districts on Sunday morning, but the water was receding on Monday as the level of the Loei River dropped. It was draining into the Mekong River.
"The water came in quickly about 5am on Sunday," Charoon Panich, mayor of tambon Nam Suay Administration Organisation, told the Public Relations Department on Monday.
Muang district chief Kittikun Butrkun said on Monday the floods had subsided but some areas in the municipality still did not have power. Repair crews were fixing that, the Public Relations Department reported.
Loei was the province most damaged by flooding on Sunday, with about 700 households affected, according to the Disaster Prevention and Mitigation Department update issued on Monday.
Three northeastern and six northern provinces, including Chiang Mai and Loei, bore the brunt of the storm.
The Meteorological Department issued another weather alert, but said Sinlaku was weakening as it entering Pua district of Nan on Monday morning. Heavy rain was expected in at least 44 provinces, most of them in the northern and northeastern regions, until Tuesday.
Floods hit San Sai district of Chiang Mai on Sunday night.