Bangkok vulnerable to floods, Thai PM Yingluck warns
All parts of Bangkok are now vulnerable to flooding, Prime Minister Yingluck Shinawatra has warned.
In a televised address, she warned that parts of the capital could be inundated by up to 1.5m (5ft) of water.
Hundreds of people who had been evacuated to the city's second airport, Don Muang, are now being moved again after flood waters reached the runway.
More than 360 people have been killed and 100,000 displaced by the country's worst flooding in more than 50 years.
The crisis is an early test for the prime minister, who took office in August and has previously been criticised for failing to take the flood threat seriously enough.
But any lingering sense of complacency has long gone, says the BBC's Rachel Harvey in Bangkok.
The water's steady progress now seems unstoppable, our correspondent adds.
In Prime Minister Yingluck's address late on Tuesday, she warned that existing floodwalls and embankments in the north of the city and around the Chao Phraya river, which snakes through the capital, were especially vulnerable.
She cautioned there could be a calamitous combination of flood waters running into the sea from north of the capital with monthly high tides on Friday and Saturday which could overwhelm recently reinforced flood defences.
She said flood waters could linger in the capital for between two weeks and a month, but said it would not be as bad as in some provincial areas, which have been under 2-3m of water for up to three months.
At present most of the city is dry.
But water levels in the Chao Phraya river reached between 2.35m and 2.4m above sea level on Tuesday, Bangkok Governor Sukhumbhand Paribatra was quoted as saying on the Bangkok Post news website.
If the surge continues, the level will reach 2.6m this weekend, he said - but river embankments are only 2.5m high.
"The high water level in the Chao Phraya river is unprecedented," Mr Sukhumbhand reportedly said.
A five-day holiday in Bangkok and flood-affected provinces begins on Thursday, with residents urged to relocate to higher ground or leave the city if they have the means to do so.
In the city of nine million, there were reports that some shops were rationing stocks of staples including rice and eggs amid stockpiling by anxious residents.
Supplies of bottled water were said to be running low in many areas.
Residents were protecting their homes and businesses with sandbags - with some even erecting sealed cement barriers across shop fronts, reported the Associated Press news agency.
At Bangkok's second airport, Don Muang, people living in an evacuation shelter are now being moved again.
All flights have already been suspended until next Tuesday, and the runway is flooded.
But the government's flood relief operation centre, which is based on the second floor of the airport, insists it will not relocate.