Two people were slightly injured after a dormitory on Soi Ramkhamhaeng 39 in Bangkok's Wang Thonglang district sank about one metre into the ground late on Tuesday night, police said.
The incident occurred at about 10.20pm. The dormitory is a two-storey concrete building with 20 rooms.
At the time of the incident, about 50 people of 19 families were in the building. All of them managed to flee from the building. Only two men -- Somchai Nongse, 46, and Nonprawit Chanrisa, 30 -- were slightly injured by pieces of broken concrete walls and other objects, including awnings.
A resident said he heard the noise of concrete walls cracking early in the night. The building started to subside at about 10.20pm. The first floor sank about one metre into the ground.
Wang Thonglang police, district officials and rescuers went to scene for examination.
Chitlada Thanongsak, the Wang Thonglang district director, said the dormitory was built 20 years ago on a land plot which was formerly a rice field. Therefore, it was initially believed the sinking was caused by land subsidence.
Checks would be carried out to see whether the building had been illegally extended.
Mrs Chitlada said she had ordered the building be declared off-limits.
Public works officials were to examine the building from 9am on Wednesday. The owner of the dormitory would also be questioned, she said.