Parts of Bangkok could still be flooded next year, Thailand's prime minister said on Tuesday, despite waters receding significantly in some areas of the city after weeks of inundation.

Thailand's worst floods in half a century, caused by months of unusually heavy monsoon rains, have left at least 562 people dead and damaged millions of homes and livelihoods around the country.

In an effort to spare Bangkok's economic and political heartland, authorities have been trying to drain the floods through waterways in the east and west of the sprawling capital of 12 million people, and out to sea.

But while Bangkok's centre has remained dry, it could be a number of weeks before the entire capital is free from the floodwaters, according to Prime Minister Yingluck Shinawatra.

"Personally I want to see people happy in the new year, but I am not confident about western areas, where it is difficult to drain water," she told reporters, when asked whether the floods would go on into 2012.

She said that eastern areas were likely to be dry before the new year.

"The general situation is stable as floodwaters drain into the sea, but how quickly it drains depends on the contours of each area," Yingluck added.

On Monday, angry residents in the city's flooded west protested by briefly blocking a major highway, as frustration mounted that parts of the Thai capital are suffering badly while the centre stays dry.

Around 70 people also gathered at a major floodwall in northern Don Mueang district, watched by about 30 police officers, to stop authorities repairing a gap they had opened to allow water to drain away from badly flooded areas.

A spokesman for the Flood Relief Operations Centre (FROC), the government agency charged with dealing with the floods, said a compromise had been struck to partially repair the eight-metre (26-foot) breach.

Yingluck, who only came to power in August and has come under intense pressure over her management of the flood crisis, insisted again on Tuesday that she had worked "with good intention and to the best of her ability".

US Secretary of State Hillary Clinton, due to visit the flood-hit kingdom on Wednesday, will offer a "very substantial" aid package to Thailand, the State Department has said.