Thai authorities are hunting a man shown on security footage strolling into a packed religious shrine and placing a bomb-laden backpack under a bench, before an explosion that killed at least 20 people.
The attack occurred on Monday in one of the Thai capital's most popular tourism hubs, ripping 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, with Chinese, Hong Kong, Singaporean, Indonesian and Malaysian citizens among the 20 confirmed killed, police said.
British authorities confirmed a Hong Kong resident with a British passport was killed, but it was not immediately clear if she was a dual national already counted among two Hong Kong victims.
More than 100 other people were wounded 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 on Tuesday branded the bombing the "worst ever attack" on Thailand, as he said 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 on a motorcycle taxi, and the blast occurred three minutes later.
"It is quite clear that he is the perpetrator in this case," Prawut told local television station Channel 3, adding police were also trying to track down the motorcycle taxi driver.
Prawut did not reveal if they knew of a motive for the attack.