Thai authorities say they are hunting a man shown on security footage strolling into a packed religious shrine and planting a bomb-laden backpack before an explosion that killed at least 20 people.
Monday's attack in one of the Thai capital's most popular tourism hubs ripped through a crowd of worshippers at the Hindu shrine close to five-star hotels and upscale shopping malls.
At least 11 of the victims were foreigners from China, Hong Kong, Singapore, Indonesia and Malaysia, but no Australians were among the dead.
More than 100 other people were injured as the blast left body parts, shattered glass and incinerated motorcycles strewn across the crushed concrete of a busy intersection.
Junta chief Prayut Chan-O-Cha said the bombing was the "worst ever attack" on Thailand and that the hunt was on for the bomber filmed on closed-circuit television at the shrine.
Police released images showing the man, who appeared young and slightly built, and wearing a yellow T-shirt and dark shorts, walking into the shrine with a backpack.
He sits down and places the backpack underneath a bench, then walks away from the shrine clutching a blue plastic bag while reading what appears to be a smartphone.
National police spokesman Prawut Thavorn said the man left the scene aboard a motorcycle taxi, which are common in Bangkok, and the blast occurred three minutes later.