At least 27 people have been killed and 78 wounded by a bomb blast that hit the commercial centre of the Thai capital Bangkok, the Reuters news agency and local media have said.
The blast, which was said to have taken place near the Erawan Shrine, occurred about 7.10pm local time, according to the Bangkok Post.
At least four foreigners were among the 27 dead in the blast, Reuters reported.
Nearby offices have reportedly been evacuated, according to reports on social media.
The bomb was placed inside the Erawan Shrine area, Defence Minister Prawit Wongsuwon said.
"It was a TNT bomb... the people who did it targeted foreigners and to damage tourism and the economy," said Wongsuwong.
Thai police said a second bomb is being defused inside the shrine.
Al Jazeera's Veronice Pedrosa, reporting from the scene, said that rescue workers have told journalists that a secondary device has been found inside the shrine itself and the bomb squad are diffusing it.
Eric Seldin, of Thaicom Production Services, was 100 metres away when the explosion happened.
"I was inside the Hyatt hotel having dinner when we heard an extremely loud explosion near the Ratchaprasong intersection," he told Al Jazeera. "The windows were shattered and everyone at the hotel was startled.
"Security tried to shut down the hotel and attempted to keep everyone inside but I was able to go out and walk just about 50 metres close to the intersection.
"I noticed seven to eight covered bodies. There was damage to the ground of the shrine.
"On the street itself there were several casualties. There is a large security presence. Police are moving people back because they are worried about the second explosion.
"The area is extremely close to the National Police Headquarters and the police hospital," Seldin said.
The bomb squad is also on the scene of the blast, possibly looking for any other devices. There has been no 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.
Thai rescue workers carry an injured person after a bomb exploded outside a religious shrine in central Bangkok [AFP]
No claim of responsibility
The bomb squad is also on the scene of the blast, possibly looking for any other devices. There has been no claim of responsibility.
A statement attributable to the Spokesman for the Secretary-General on Thailand said:
"The Secretary-General was shocked to learn of the explosion in Bangkok today close to the Erawan shrine and the loss of life of innocent civilians.
"He expresses his condolences to the bereaved families and to the people and Government of Thailand, and wishes those injured a quick recovery. He hopes that those responsible will be brought to justice."
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.
Al Jazeera spoke to people at the scene of the explosion.
Somrudee Prayunwong [Al Jazeera]
Somrudee Prayunwong, Resident
We don't want to think about what will happen next - the death toll has been rising so quickly, we're afraid to think about how bad it could be.
We live near here. We didn't think it would be a bomb, we thought something else had happened.
Prayoong Supharot [Al Jazeera]
Prayoong Supharot, Motorcycle Taxi Driver
At 6pm I heard something that sounded like thunder. But it turned out to be something much worse - something that never should have happened. So a bunch of us motorcycle taxi drivers who were by the intersection went into a hotel nearby to hide.
When we heard there was an explosion we became frightened, and each of us went to find out own hiding spaces.
After the explosion there was silence. Then we all went out to see what had happened. We saw body parts scattered all over - corpses of people... we couldn't tell what nationalities they were.
At first we saw that five people had died - then it turned out to be more than we had expected. It felt like something that shouldn't have happened - right in the heart of the city. We don't know why it happened, but of course everyone is frightened now.
Malee Roongrueng [Al Jazeera]
Malee Roongrueng, Street Vendor
This doesn't affect me that much, I'm pretty used to all this - I've seen the red shirt protests, I've seen bombs in telephone booths.
I was nearby when I heard the blast - I thought it was thunder. Then I walked back and someone told me it was a bomb - I was shocked!


Notes from the field:

Not too long after the blast, the police started to cordon off the area. As I was walking away I saw one of the officers picking up what looked like little cotton pads that were soaked in blood - probably a leftover from someone trying to treat one of the wounded in the aftermath of the blast.
At the spot of the blast there was a motorcycle on the street, blown into at least two pieces. Officials in the area were looking around for more bombs - I kept hearing that more bombs had been found - there were a lot of rumours going around.
Soon, all of the press and passersby gathering in the area had to move further and further away - they were expanding the search area for more bombs - the area was not risk-free.