Hungry diners remained unfazed - calmly tucking into their bowls of noodles even as floodwaters gushed into an eatery in Thailand.

Footage shows the customers tucking into lunch despite the knee-level floods flowing into the streetside restaurant in Khon Kaen province on September 9.

Outside, torrential rains battered the neighbourhood, inundating the streets with debris-filled water.

The Thai Meteorological Department had issued a severe thunderstorm warning for 41 Thai provinces, including Bangkok, warning of severe rain and flood.

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.