Large-scale evacuation was underway in Bang Phlad, a riverside area some way from Bangkok's inundated northern districts, as floods hit the capital on a second front, deepening anxiety in the city of 12 million people, many of whom were expected to flee before a special five-day holiday.
"Now we're at a critical moment, we need to monitor the situation closely from 28-31 October, when many areas might be critical," Bangkok Governor Sukhumbhand Paribatra told reporters on Wednesday. "Massive water is coming."
Sukhumbhand said 90 percent of the northern Don Muang district was under water and Bang Phlad was in a critical situation. Fourteen city districts were threatened by floods and two more could be hit on Thursday, he said.
Thailand's worst flooding in half a century has killed at least 373 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.
Bangkok residents scrambled to stock up on food, but bottled water was nowhere to be seen and some shops restricted customers to small quantities of food to prevent hoarding. Bus stations were packed as thousands prepared to leave the city.
With 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. The finance minister's projection was a gloomier 2 percent.
Prime Minister Yingluck Shinawatra, who said two weeks ago that Bangkok was likely to escape the floodwaters, said on Wednesday that it could be flooded for as long as a month.
"But we shouldn't face water as high as two or three metres or staying for two or three months as we've seen in other provinces," she told reporters.
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 agreed on Tuesday on a 325 billion baht ($US10.6 billion) budget to rebuild the country, while city authorities and the Commerce Ministry were meeting with industrial estate operators, hotels 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 Thailand's gross domestic product.
The floods are expected to take a toll on Thailand's tourism industry, which employs more than 2 million people and makes up 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 vehicles driving at a snail's pace through 1.5 metres of water, ferrying evacuees away on roads shared by cars and boats.
Some people were being evacuated for a second time, with 4000 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 pumped an estimated 8 billion cubic metres of water daily through canals and a river around Bangkok's east and west 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.
Water has engulfed two areas, with levels climbing higher than half a metre in the densely populated Bang Phlad district near to the Chao Phraya and closer to the commercial heart.
Overloaded trucks shuttled out evacuees from Bang Phlad, gas stations were inundated and shop owners pulled down shutters and added sandbags to makeshift defence walls.
"My shop is damaged. I've prepared for this, but it's not enough -- there's too much water," said grocery store owner Vichit Pookmaitree.
As panic grew, 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.
