“It was a TNT bomb… the people who did it targeted foreigners and to damage tourism and the economy,” Thailand’s Defence Minister Prawit Wongsuwong said, Channel News Asia reported.
Most of those injured in the explosion were said to be predominantly Asian tourists, with the majority taken to Police General Hospital and Chulalongkorn Memorial Hospital.
No one has claimed responsibility for the attack.
A number of foreign nationals were injured in the blast, according to witnesses.
The Bangkok Post quoted police as saying that at least one more bomb was defused by officers in Ratchaprasong area.
Local TV showed burnt motorbikes on the main road, with paramedics and police taking the injured away.
The explosion was on the Rajprasong intersection, which has been the centre of political demonstrations in recent years.