A flash flood surged under a wooden bridge as torrential rains battered a national park in Thailand.

Rivers and waterfalls swelled at the Doi Inthanon National Park in Chiang Mai province, prompting authorities to close the spot to tourists starting September 16.

Footage shows the raging deluge roaring under a wooden walkway as it threatened to submerge the structure. Heavy floods were also seen cascading down a waterfall inside the park.

Authorities said the area saw an average of 65 to 164 millimetres of rainfall, with the highest amount recorded at the summit of a mountain in the park.

Officials have warned residents in neighbouring Chom Thong district to be vigilant of flash floods and landslides.

Local media reported that runoff from the national park had flowed into the Mae Klang River, causing it to burst its banks and flood surrounding agricultural land and roads.

Officials were surveying the area to determine the extent of the damage.

Thailand and neighbouring countries in Southeast Asia are in their annual monsoon rainy season which sees soaring temperatures followed by powerful rain storms in the afternoon leading to widespread flash floods.