Thailand raced on Tuesday to build floodwalls on the outskirts of Bangkok to prevent the worst floods in half a century from inundating parts of the capital later this week when water flowing from the north reaches the low-lying city.

At least 269 people have been killed by heavy monsoon rains, floods and mudslides that have battered 27 of Thailand's 77 provinces since late July, according to the Department of Disaster Prevention and Mitigation.

Much of Thailand's north, northeast and central plains are flooded, affecting 2.3 million people.

Bangkok - only two meters above sea level - could be next if water overflowing from reservoirs in the north arrives at the same time as high estuary tides are due from Oct 13.

Rescue workers hastily built a floodwall in Pathum Thani, north of Bangkok, where strong currents burst a river embankment overnight, flooding homes in water at least two meters high.

"I've never seen floods as bad as this year. The first floor of my house is all flooded, and it's coming up to the second floor," said Wanpen Suanmakam, 62, a resident in Pathum Thani, a province intersected by canals that feed its rice paddies.

Another resident, Sukanna Saeieaw, 60, almost up to her neck in water, said a makeshift walkway briefly helped people avoid water when the road was flooded but it was quickly washed away.

"The water came in very fast," she said.

Lerpong Kaewsrichan, Pathum Thani deputy governor, said the water had mostly submerged farmland, but two industrial estates in the area had been spared for now.