The government is stepping up its investigation into other construction projects linked to the Chinese contractor of the State Audit Office's (SAO) under-construction building that collapsed in Bangkok during last Friday's earthquake.

Prime Minister Paetongtarn Shinawatra said she told various agencies to investigate all construction projects awarded to China Railway No.10 Engineering Group.

The SAO contracted a consortium of Italian-Thai Development Plc and China Railway No.10 to construct the 2.1-billion-baht building.

She said the collapsed building has cost lives and negatively affected Thailand's image.

"All buildings in Bangkok must meet legal standards. Safety must be the top priority," she said.

Apart from the SAO building, other projects undertaken by China Railway No.10 Engineering Group include the construction of a building of the Office of the National Water Resource and some sections of the Bangkok-Nong Khai high-speed railway project.

Bloomberg reported that the contractors of the under-construction office tower which collapsed in Bangkok used substandard steel bars made by a factory that had been closed by authorities.

The 30-storey building was the only building to crumble in the Thai capital in the wake of the 7.7-magnitude earthquake that hit Myanmar. The collapse killed at least a dozen workers and trapped dozens more.