Fears of flooding across the Thai capital have grown after the Thai prime minister said that parts of Bangkok could face inundation for up to a month and experts pinned the city's fate on dykes along the Chao Phraya River.
Yingluck Shinawatra says that central Bangkok could be swamped by up to 1.5 metres of water in some places if barriers broke and told residents to get their belongings up to high ground.
"After assessing the situation, we expect floodwater to remain in Bangkok for around two weeks to one month before going into the sea," she said on Wednesday.
"However, the situation shouldn't be serious as in other provinces. We shouldn't face water as high as two or three metres staying for two or three months as we've seen in other provinces."
Authorities would guard important places such as the royal palace and power stations, she said.
The Thai government has also declared a holiday from October 27 to 31 to allow people in the hardest-hit areas to evacuate their homes at a time of expected high estuary tides on the Chao Phraya river.
The floods in the north, northeast and centre of Thailand have killed at least 366 people since mid-July and disrupted the lives of nearly 2.5 million, with more than 113,000 in shelters and 720,000 people seeking medical attention.
Authorities are scrambling to pump out water around the east and west of Bangkok, but record-high water levels in the Chao Phraya River that winds through the city raise the risk of floods in the commercial heart when the high tides come.
Seri Supharatid, director of Rangsit University's Centre on Climate Change and Disaster, said the city's fate rested on dykes along the Chao Phraya River.
Wayne Hay reports on the latest developments
"In the worst-case scenario, if all the dikes break, all parts of Bangkok would be more or less flooded," Seri said.
Flooding has already forced the closure of seven industrial estates, causing billions of dollars of damage, disrupting international supply chains for industry and putting about 650,000 people temporarily out of work.
Residents have cleared supermarkets of bottled water and are hoarding food such as rice and instant noodles.
In some areas, people are complaining about deterioration in the quality of tap water, which is normally potable but now has a yellowish colour and a bad smell.
The Metropolitan Waterworks Authority said that floodwater has broken through temporary dikes in places into a
raw water canal used for producing tap water.
"However, we've put in chemicals in order to kill contaminated organic substances in the water to make it cleaner.
We expect to solve this problem within a couple of days," it said on its website.
TV footage on Wednesday showed people wading knee-high alongside the river by the Grand Palace, one of the main tourist attractions in Bangkok.
Chumphol Silpa-archa, Thailand's tourism minister, said tourist arrivals could be 500,000 to one million below the government's target of 19 million this year because of the floods.
Don Muang airport, used by budget airlines for domestic flights and by private planes, had to close on Tuesday due to flooding that was making access to the area difficult.
By Wednesday, floodwater had reached the runway, Thai media said. The government has its flood-crisis centre in the airport.
The main Suvarnabhumi Airport has not been affected because it is on higher ground and protected by an earthen dyke, but Thai Airways International said it may reduce flights from there because of staff shortages.