Bangkok's second airport has suspended all flights after floodwaters breached its northern perimeter.
Don Muang airport, used mainly for domestic flights, is in northern Bangkok - the area of the capital worst hit by the flooding.
The international airport, in another part of the city, is still operating.
Thailand has been hit by heavy monsoon rain since July, leading to flooding which has hit swathes of the country and left more than 360 people dead.
Water from inundated central areas is now running south to the sea.
Officials have been trying to drain it to the east and west of Bangkok, but they have been forced to open sluice gates into the city because of the sheer volume of water building up outside Bangkok's flood barriers.
On Tuesday, the Thai cabinet announced a 325bn-baht ($10.5bn; £6.6bn) fund to help rebuild the country - mainly aimed at small and medium businesses, small vendors and individuals, reported Reuters news agency.
"If they get back to normal quickly, it will help push the economy forward," the agency quoted Finance Minister Thirachai Phuvanatnaranubala as saying of the businesses.
Seven districts of the capital are now said to be at risk - with Bang Phlad, home to department stores, universities and hospitals, added to that list by Bangkok Governor Sukhumbhand Paribatra late on Monday.
Central areas remain dry, but the Chao Phraya river, which bisects the city, reached a record high on Monday.
Don Muang airport - a hub for domestic flights, low-cost carriers and some cargo - has been threatened by encroaching floodwater for several days.
An official said the flooding was affecting perimeter areas, not the runway. However the runways are not expected to reopen for a week.
There were chaotic scenes at the airport, reported Associated Press news agency, with throngs of confused passengers in the departure hall and long waiting times for transport.
The airport is also now being used as an evacuation centre and as the headquarters of the government's flood relief operations. Relief officials said they had no plans to relocate.
Elsewhere, residents of the Muang Ake housing estate were ordered to evacuate after a flood protection wall in nearby Pathum Thani province was breached, Reuters reported.
Thai authorities have declared a holiday in several provinces, including Bangkok, to help people cope with the flooding.
Schools and offices will close from Thursday through to the end of Monday, creating a five-day break.
Are you in the region? Have you been affected by the flooding? Have you been forced to leave your home? You can send us your stories and experiences using the form below.
Send your pictures and videos to email@example.com or text them to 61124 (UK) or +44 7624 800 100 (International). If you have a large file you can upload here.
If you are happy to be contacted by a BBC journalist please leave a telephone number that we can contact you on. In some cases a selection of your comments will be published, displaying your name as you provide it and location, unless you state otherwise. Your contact details will never be published. When sending us pictures, video or eyewitness accounts at no time should you endanger yourself or others, take any unnecessary risks or infringe any laws. Please ensure you have read the terms and conditions.