The Thai police radio reported that the cause of the explosion was not clear.
Witnesses said the explosion took place around 7:15 local time at the Rajprasong Intersection, a business area famous among tourists and locals for a revered Hindu shrine.
Eric Seldin, an office worker, said he was having his dinner at the Hyatt Erawan Hotel when a large explosion shook the building.
He said five minutes later when they were all evacuated from the hotel they saw several bodies covered under white sheets and damage to a nearby shrine.