The government said the blast was an attack aimed at destroying the economy. Local media reported that foreign tourists were among the dead.
There was no immediate claim of responsibility for the blast at the Erawan shrine at a major city-centre intersection. The shrine, on a busy corner near top hotels, shopping centres, offices and a hospital, is a major tourist attraction.
“The perpetrators intended to destroy the economy and tourism, because the incident occurred in the heart of the tourism district,” Defence Minister Prawit Wongsuwan told Reuters.
Reports said that a second bomb had been found in the area and made safe.
“It was like a meat market,” said Marko Cunningham, a New Zealand paramedic working with a Bangkok ambulance service, who said the blast had left a two-metre-wide crater.
“There were bodies everywhere. Some were shredded. There were legs where heads were supposed to be. It was horrific,” Mr Cunningham said, adding that people several hundred metres away had been injured.