A bomb has exploded close to a shrine in the centre of Thailand's capital, Bangkok, killing at least 16 people and injuring more than 80.
Reports say a second bomb has been found in the area and made safe.
No-one has yet said they carried out the attack, which took place close to the Erawan shrine in Bangkok's central Chidlom district.
The shrine is a major tourist attraction. The Thai government said the attack was aimed at foreigners.
Local media report that tourists, including Chinese, may be among the casualties.
Defence Minister Prawit Wongsuwong said: "It was a TNT bomb... the people who did it targeted foreigners and to damage tourism and the economy."
The Nation TV channel quoted Prime Minister Prayuth Chan-ocha as saying the government would set up a "war room" to co-ordinate its response.
Nation put the death toll as high as 27, saying at least three foreigners were killed, but there is no official confirmation.
The explosion occurred at about 19:00 local time (12:00 GMT).
The Bangkok Post said there were twin blasts - one from a motorcycle bomb and the other from a device fixed to an electricity pole. It quoted police as saying 5kg of TNT was used and that an electronic circuit suspected to have been used in the attack was found 30 metres from the scene.
The BBC's Jonathan Head, who is at the scene, says there is a huge amount of chaos, with body parts scattered everywhere.
He says this is a very well-known shrine in the centre of Bangkok, next to a five-star hotel, and that people around the shrine were hit by the full force of the blast.
One bystander, Alessandro Ursic, told the BBC: "When I arrived they had already cleared the bodies from the ground outside the Erawan shrine but there were and there are still pieces of human flesh strewn around the intersection; it's really graphic."
Another, James Sales, said: "I went into where the shrine is, where there were lots of bodies. I saw at least nine people unfortunately who looked like they had died and lots of Chinese tourists as well.
"I tried to administer CPR to one particular guy who was in his 40s... and he didn't make it."
The shrine is dedicated to the Hindu god Brahma, but is also visited by thousands of Buddhists each day. There are also three major shopping centres nearby.
National police spokesman Lt Gen Prawut Thavornsiri told Agence France-Presse news agency: "I can confirm it was a bomb, we can't tell which kind yet, we are checking."
The explosion was on the Ratchaprasong intersection, which has been the centre of political demonstrations in recent years.
Our correspondent says bomb attacks in Bangkok are extremely rare.
There has been a Muslim insurgency, but this has been largely confined to the south of the country and attacks rarely take place elsewhere.
But Bangkok has seen a decade of sometimes violent rivalry between political factions.
The military took over ruling the country in May last year, removing an elected government following months of unrest.