Preliminary investigations showed the mechanics were working on the lift on the 25th floor of the Saeng Thong Thani building, where Citibank has its Thai headquarters, when it suddenly plunged to the basement, Major Archawin Boontham-charoen of Thung Mahamek police station said.

Witness Kriengkrai Meesaeng said all four mechanics had worked for the Hitachi maintenance team.

He said that after using a sling to suspend the lift, the three victims had been on its roof without safety ropes while the only survivor, Thani Khamhom, had been inside.

Kriengkrai said Thani had managed to throw himself out but his right arm had been trapped by the falling lift.

Police investigations are continuing.