Flood warnings have been issued for five northeastern provinces where the rapidly rising Mekong River could burst its banks.
The Office of the National Water Resources said on Tuesday a huge volume of floodwater was flowing downstream and could cause flooding this week in Bung Kan, Nakhon Phanom, Mukdahan, Amnart Charoen and Ubon Ratchathani provinces.
Many parts of Nong Khai province have already been inundated by overflow from the swollen Mekong.
The municipal area in Muang district is among the worst flooded. All business there has been brought to a standstill over the past few days.
The flood level is dropping but the municipal office on Tuesday again put up a red flag in some communities and strongly advised people there to keep themselves updated on the situation.
Some parts of the town are still closed to traffic after the strong flood current eroded road surfaces.
In Nakhon Phanom, the Mekong was continuing to rise but municipal mayor Niwat Chiawiriyabunya was hopeful they could keep the city dry. He said the water level in the river was still three metres below the crisis point.
Residents and vendors along the Mekong banks have been advised to move to higher ground and Nakhon Phanom stadium has been prepared for use as a temporary shelter if needed, he said.
The Mekong flows into southern Laos after leaving Ubon Ratchathani.
New storm warning
The Meteorological Department on Tuesday warned that heavy rain is likely across the country, with strong winds and high tides along the Andaman coast and in the upper Gulf of Thailand until Friday.
The weather office said it was watching a low pressure system to the east of the Philippines that could gain strength and develop into a tropical storm before it makes landfall in northern Vietnam on Friday.
This could bring more heavy rain to much of Thailand.
Seasonal flooding has killed 22 people, 12 of them in Chiang Rai province, since mid-August, according to the Disaster Prevention and Mitigation Department.