Flash floods battered roads amid torrential rains in northern Thailand.

Footage shows a swollen river submerging a bridge in Nan province at 6:40 am local time today.

The surging deluge spilled onto nearby streets and homes, swamping Ban Hat Ra village with up to 20 inches of flood and rendering roads impassable.

Residents in Ban Nam Muap village were forced to evacuate as the floodwaters reached up to three feet.

The Department of Disaster Prevention and Mitigation said several districts were at a 'critical warning' level as heavy rains pummeled the province.

The Thai Meteorological Department forecasted that northern Thailand, including Nan, would experience widespread thundershowers and isolated heavy to very heavy rains.

Thailand and neighbouring countries in Southeast Asia are at the start of their annual monsoon rainy season which sees soaring temperatures followed by powerful rain storms. The rudimentary infrastructure often struggles with the deluge, leading to widespread flash floods.