UPDATE 2.30PM: Further bombs have been set off in locations across Thailand and at least four people are believed to have been killed. 

A series of bombs, believed to be IEDs, set off just hours after two other devices hit a Thailand tourist spot. 

Up to eight bombs are believed to have been set off, with even more defused by local police. 

Locations targeted in the attacks include tourist towns and Phuket. 

EARLIER: One woman has died and at least 20 other people are injured following two bombs at a tourist resort in Thailand, local media has reported.

The severity of their injuries is not yet known.

It is understood the double explosion took place after the devices were hidden in plant pots and detonated remotely using mobile phones.

British tourist Mark Gainsford told the BBC he had been in a bar near the twin blasts.

"I heard people shouting 'Bomb! Bomb!' but I didn't hear any blast," he said.

"I ran out to see if I could help. I saw eight to 10 people injured, on the floor. The police arrived very quickly."

Police are investigating and as yet do not know the motive or the identity of the bombers.

The explosions happened ahead of a public holiday on Friday to mark the birthday of Queen Sirikit.

Hua Hin is a popular upscale Thai resort south of Bangkok and many people will have gone there for the holiday weekend.

The resort town Hua Hin is popular with tourists in the area.

Local media outlet ThaiPBS tweeted what appeared to be a photo showing emergency services tending to the injured in a hospital.

And reports on the web sites of the Thai Rath newspaper and other media said the bombs were hidden in planters on a busy street with open-front bars.

The reported fatality was a female street food vendor.

It was not clear who was behind the attack, but the timing suggested it might be an effort to embarrass the military government that took power two years ago.

In another photo posted by the public broadcasting service, ambulances and police cars appeared to be stationed at the scene.

Hua Hin is about 120 miles (200km) south of Bangkok.