Shops in the Thai capital began imposing emergency rationing on Wednesday as the prime minister warned parts of Bangkok could be flooded for up to a month and authorities called a special five-day holiday to give people the chance to flee.
An evacuation warning to residents of a riverside district some way from swamped northern parts of the city deepened anxiety in the city of at least 12 million people, where residents scrambled to stock up on food and water.
After assessing the situation, we expect floodwater to remain in Bangkok for around two weeks to one month before going into the sea, Yingluck told reporters.
However ... 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.
Thailand's worst flooding in half a century has 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.
With a high tide approaching in the Gulf of Thailand, Seri Supharatid, director of Rangsit University's Centre on Climate Change and Disaster, said the city's fate rested with river dykes holding.
In the worst-case scenario, if all the dykes break, all parts of Bangkok would be more or less flooded, Seri said.
The economic damage is difficult to quantify, but the central bank has revised its growth forecast for Southeast Asia's second-biggest economy to 3.1 percent this year from 4.1 percent earlier this month. The finance minister's projection was a gloomier 2 percent.
Flooding has forced the closure of seven industrial estates in Ayutthaya, Nonthaburi and Pathum Thani provinces bordering Bangkok, causing billions of dollars of damage and disrupting international supply chains for industry and putting about 650,000 people temporarily out of work.
The cabinet on Tuesday agreed on a 325 billion baht (6.6 billion pound) budget to rebuild the country, while city authorities and the Commerce Ministry were meeting with industrial estate operators, hotel chains, businesses and food producers to try to minimise the damage and kick-start a recovery.
Authorities have called a holiday from Thursday until Monday to allow people to get out Bangkok, although financial markets will remain open.
The rising tide could complicate efforts to drive water from the swelling Chao Phraya river out to the sea, putting more pressure on a city that accounts for 41 percent of the country's gross domestic product.
Heavy rain could also deepen the crisis and thunderstorms were forecast for Wednesday.
The floods are expected to take a toll on Thailand's tourism industry, which employs more than 2 million people and accounts for roughly 6 percent of GDP. Tourism Minister Chumphol Silpa-archa said arrivals could be 500,000 to 1 million below the government's target of 19 million this year.
Three northern districts of Bangkok have been under water since Saturday, with army trucks driving at a snail's pace through 1.5 metres of water, ferrying evacuees away.
Some people were being evacuated for a second time, with 4,000 sheltering in Don Muang moving to the province of Chon Buri. Evacuees at a university in Pathum Thani province also had to move on as floodwater engulfed the campus.
To tackle the flooding, the authorities have been pumping an estimated 8 billion cubic metres of water daily through canals and a river around the east and west of Bangkok towards the sea.
But the large volume of water flowing through the city remains a concern, with the vast Chao Phraya river at record levels and running past high-end hotels, embassies and the Sathorn and Silom areas of the city's business district.
Governor Sukhumbhand Paribhatra on Tuesday warned there was danger of flooding on a second front, with the densely populated Bang Phlad district near to the Chao Phraya and closer to the commercial heart now a high-risk area.
Bang Phlad is in a critical situation. We will look after all the residents as best as we can, but we ask everyone to move to the evacuation centres, Sukhumbhand told reporters.
Central Pinklao, a department store owned by Central Pattana Pcl, situated close to the river had to close.
As panic mounted, shoppers at a central Bangkok hypermarket run by Big C Supercenter Pcl were being restricted to one packet of rice and one tray of eggs. Toilet paper was also being rationed. Bottled water had run out.
In some areas, people are already complaining about a deterioration in the quality of normally drinkable tap water.
The Metropolitan Waterworks Authority said floodwater had got into raw canal water used for its supply. Chemicals were being used to purify it.
Shares in Thai beverage firm Haad Thip Pcl surged more than 6 percent on Wednesday on expectations the company would benefit from the huge demand for drinking water.
(Writing by Alan Raybould and Martin Petty)