He added: "There could be another explosion, so we have blocked off the crime scene and are asking bystanders to move back."
Burnt motorbikes lie in the road after the blast
AFP/Getty Images
The explosion took place at the Rajprasong intersection, which has been the centre of political demonstrations in recent years.
Thailand's capital has been relatively peaceful since a military coup ousted a civilian government in May last year, after months of sometimes violent political protests against the previous government.