The blast was near the Erawan shrine at a major Bangkok intersection, police said.

"All I can say now is there has been an explosion in central Bangkok involving a motorcycle bomb," deputy national police chief Aek Angsananond told Reuters. He said there had been fatalities, but could not confirm details.

Officials said 12 people had been killed.  Several were foreigners. Most of the injured were tourists from China and Taiwan, media said.

A Reuters witness at the scene said she saw pieces of human flesh near the blast site, and a soldier later told onlookers to move back, saying they were checking for a second bomb.

There was no immediate claim of responsibility. Thai forces are fighting a low-level Muslim insurgency in the predominantly Buddhist country's south, although those rebels have rarely launched attacks outside their ethnic Malay heartland.

The country has also been riven for a decade by intense and sometimes violent rivalry between political factions in Bangkok and elsewhere.

The army has ruled Thailand since May 2014, when it ousted an elected government after months of, at times, violent anti-government protests.

The Erawan shrine, on a busy corner near top hotels, shopping centres and offices, is a major tourist attraction, especially for visitors from East Asia. Many ordinary Thais also worship there.