Tourists are being warned to "exercise extreme caution" in Thailand after a wave of co-ordinated explosions left at least four people dead and dozens more wounded.

The Foreign Office updated its travel advice following 11 blasts within 18 hours in cities and resort towns across southern Thailand, including Hua Hin, Trang and Surat Thani, Phang Nga and Patong, Phuket.

The explosions all occurred south of Bangkok and several of the blasts - including one on Patong beach in the tourist resort of Phuket, and three in the seaside city of Hua Hin - appeared designed to strike at the tourism industry. An FCO spokesman said: "There have been multiple explosions in tourist areas across Thailand on 11 and 12 August. We are in close contact with local authorities and urgently seeking more information. We stand ready to provide assistance to any British nationals involved." It is advising against "all but essential travel" to the provinces of Pattani, Yala, Narathiwat and Songkhla on the Thai-Malaysia border.

Two British nationals were said to be present at one or more of the explosions but were not thought to be injured. Meanwhile, tourists in the south-east Asian country expressed their shock following the blasts. One Facebook user wrote: "Bombs have gone off in Hua Hin but we are all safe and well. Thoughts are with families of injured and the family of the street vendor killed in the first attack last night." A️nother posted: "It really sucks what's happened here and it's scary to think about what place could be next, but my heart goes out to all that have been affected by these bombs!! Such a shame."

Among the injured were 21 people, including around 10 foreigners, in Hua Hin, which was hit by two explosions on a busy street filled with bars and restaurants on Thursday night.

A Thai woman, reported to be a market trader, was killed. There were also explosions in Trang on Thursday, killing one person and injuring six; and Surat Thani on Friday, killing one person and injuring three. Several small explosive devices were found in Phuket on Friday, injuring one person on Loma beach, while Hua Hin was rocked by another set of explosions, killing one person and injuring three.

The FCO is warning tourists to " exercise extreme caution, avoid public places, and follow the advice of local authorities". It added that it currently had no information that any British nationals were involved in the recent blasts, which t ook place on the birthday of Thailand's Queen Sirikit and overnight. It was not clear who was behind the attacks, but Thai police said the violence was not linked to international terrorism or a low-level insurgency in the country's Islamic south.