Thai workers and soldiers raced to finish defensive walls around inner Bangkok on Thursday as floodwater that has covered about a third of Thailand threatened the capital.
At least 283 people have been killed around Thailand by heavy monsoon rain, floods and mudslides since late July and in the past week several huge industrial estates north of Bangkok have been inundated, adding to the damage to the economy.
After a meeting with ministers, army chief Prayuth Chan-ocha told reporters that flood barriers in three vulnerable locations in Bangkok had almost been completed.
"We talked about evacuation plans to help people living near the Chao Phraya river. If there's an emergency, we're ready to act," he said.
"The worry now is that from today until 19 October there will be a high tide and the important thing is to push water out to the sea as fast as possible."
Bangkok accounts for about 41 per cent of Thailand's economy and any serious disruption to life in the capital could cause growth forecasts to be slashed further.
Consumer confidence fell in September because of the floods and could plunge in October, according to economists at the University of the Thai Chamber of Commerce.
Last week, the university cut its forecast for GDP growth this year to 3.6 per cent from 4.4 per cent and then cut it again on Thursday to 3.0-3.5 per cent.
The Finance Ministry has cut its growth forecast to 3.7 per cent from 4.0 per cent.
The province of Ayutthaya to the north of Bangkok has been badly hit and at least three big industrial estates there have closed temporarily. A Nikon Corp digital SLR factory and a Honda Motor Co Ltd assembly plant have closed.
The north, northeast and central plains of Thailand have been worst hit and Bangkok -- which is only two metres (6.5 ft) above sea level -- is in danger as water overflows from reservoirs in the north, swelling the Chao Phraya river.
Some outer areas of greater Bangkok have already flooded but authorities hope the centre will be saved by existing defensive structures plus three new walls, which will help channel water to the east and west of the city into the sea.
Run-off water from the north will arrive in the Bangkok area at the weekend at the same time as high tides. This may also coincide with storms and heavy rain.
Sanya Cheenimit, director of Bangkok's drainage and sewerage department, reported flooding in three eastern districts of Bangkok that were mainly farm areas.
"I want to reassure you that the flood situation in Bangkok is still under control," he told Reuters. "All the 50 districts of Bangkok have readied evacuation plans ... But for now, there's still no sign that we need to move people out."
Despite the reassurances, residents have stocked up on bottled water and foodstuffs such as instant noodles.
More than 2 million people are estimated to have been affected by floods around the country and essential goods are in short supply in some areas because of disruption to road and rail traffic, with some main roads to the north cut off.
Hundreds of volunteers gathered on Thursday at the government's flood crisis centre at Bangkok's old Don Muang airport, loading donated water, food and medicines on to trucks to be distributed to the worst-hit areas outside the capital.
In Bangkok, authorities are most concerned about 27 communities with 1,200 households along the river.
"We are worried about all the areas near the Chao Phraya river," army chief Prayuth said.
"We've asked people not to break the flood barriers because it may cause water to overflow into Bangkok," he added.
Some residents of flooded outer areas have vented their anger at the temporary walls put up to protect the capital.
The governor of the neighbouring province of Pathum Thani called on Wednesday for a state of emergency to be declared to give the security forces power to stop such acts, but Prime Minister Yingluck Shinawatra ruled that was not necessary.