At least 18 people have been killed after a bomb exploded in central Bangkok, emergency services have said.

Media in the Thai capital suggest the death toll could be as high as 27 and that four foreigners are among the dead.

The blast happened at 7pm (1pm UK time) near the Erawan Hindu shrine in the downtown Chidlom district - a shopping hub popular among tourists.

At least 117 people have been wounded, some of whom have lost limbs.

CCTV footage showed a huge orange fireball as the bomb exploded and people fleeing down the street.

Witnesses described seeing bodies "shredded" in the street, while locals said the explosion sounded similar to a loud thunderclap.

Some reports suggest the bomb was inside the shrine, while others say it was on one of six motorcycles seen strewn across the street in the aftermath.

At least two Chinese and one Filipino are among the dead, local media have said.

There are no reports of British casualties.

The Foreign and Commonwealth Office said: "We are in contact with local authorities following an explosion in Bangkok. At this time we have no reports of British nationals killed or injured but we are urgently seeking further information."

No-one has claimed responsibility for the attack.

Defence Minister Prawit Wongsuwon said the bombers "targeted foreigners... to damage tourism and the economy".

"We will hunt them down," he added.

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Former Bangkok resident Lucinda-Jane Chastain, who was having cocktails in a hotel above the blast site, told Sky News: "The whole building shook. We all ran to the windows. It was quite hard to see what was happening but we could see debris in the street.

"All we can see is a horrible mess on the road. This is at the very heart of Bangkok."

Details of the device are now starting to emerge.

Somyot Poompummuang, Thai national police chief, said: "The blast radius of the bomb is about 100 metres. The bomb experts say that the bomb weighed about 3kg."

Terrorism expert Joe Gyte told Sky News the bomb was "a TNT-based improvised explosive devise".

The US State Department said it was too soon to tell if the blast was a terrorist attack.

State spokesman John Kirby said authorities in Thailand were investigating and had not yet requested assistance from the US.

Deputy Prime Minister Prawit Wongsuwon told reporters: "We still don't know for sure who did this and why.

"We are not sure if it is politically motivated, but they aim to harm our economy and we will hunt them down."

The shrine sits at the Rajprasong intersection which has been the centre of many political demonstrations in recent years.

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