He said: "Whoever planted this bomb is cruel and aimed to kill. Planting a bomb there means they want to see a lot of people dead."
Thai police said 123 people had been injured. The government in Hong Kong said three of its residents were among those wounded.
The explosion occurred at about 19:00 local time (12:00 GMT).
The Bangkok Post quoted police as saying that 3kg of TNT had been stuffed in a pipe inside the shrine and that an electronic circuit suspected to have been used in the attack was found 30 metres from the scene.
Police checked the area for other devices but no further bombs have been found, the paper said.
'Really graphic'
The BBC's Jonathan Head, who was one of the first journalists at the scene, said there was a huge amount of chaos, with body parts scattered everywhere.
He says this is a very well-known shrine, next to a five-star hotel, and that people around it were hit by the full force of the blast.