Receding floodwaters north of Bangkok have reduced the threat to the Thai capital, but a rise in coastal high tides in the Gulf of Thailand will still test the city's flood defences.
Bangkok's main waterway, the Chao Phraya River, has swollen close to its brink during unusually high tides, causing some flooding in nearby areas.
Buildings across Bangkok have been sand-bagged for protection.
Many residents have fled the city or stocked up on water, food, life jackets and even boats.
Thailand's worst floods in half a century have killed 377 people since July, wiped out a quarter of the main rice crop in the world's biggest exporter and caused delays in global car production after destroying industrial estates.
The floods have submerged four million acres of land turning entire cities into urban reservoirs.
Prime Minister Yingluck Shinawatra said the ebbing of floodwaters in northern provinces, thanks to the draining of water into the Gulf of Thailand through canals and pumps, had reduced the risk of large volumes of run-off water bearing down on Bangkok.
The city sits only 2m above sea level.
The Chao Phraya is expected to rise to as much as 2.6m above sea level today during high tides, the government said this week when it declared a five-day holiday from Thursday to allow people to leave.
Many foreign governments have warned their citizens against non-essential travel to the city.
Bangkok's governor ordered the evacuation of a fourth district, Thawi Whatthana, in western Bangkok.
Evacuations have now taken place in four of Bangkok's 50 districts - Don Muang, Bang Phlat, Sai Mai and Thawi Whatthana - all of which have suffered floods in recent days.
Local authorities expect Thonburi, on the west bank of the Chao Phraya, to be inundated within three days and Ms Yingluck said levels should remain high for days due to a lack of canals.
