On Thursday there were twin blasts in Hua Hin and Trang, and further explosions today in Hua Hin and Surat Thani.
The FCO said it was also “urgently clarifying reports of an incident in Phuket”, with the beach town of Patong believed to have been hit by several blasts today.
Blasts have additionally been reported in the beach province of Phang Nga in southern Thailand.
At least four have been confirmed dead by the explosions, with many more injured.
An Abta spokesman said: "Abta is aware of only very small numbers of customers on holiday with its members.
"However, Thailand is a popular destination for backpackers and independent travellers; and in 2015 there were 320,000 holiday visits to Thailand by British people."
No one has yet claimed responsibility for the attacks, but suspicion is likely to fall on separatist insurgents, the BBC said.
The timing is also particularly sensitive as today (August 12) marks the queen’s birthday.
The attacks seems to have particularly focused on tourist areas, with the Hua Hin explosions on Thursday night striking a bar area popular with tourists, and foreigners were among those injured.
The choice of Hua Hin as a target is also symbolic, the BBC noted. It is recognised as being a royal city and the king’s favoured residence outside Bangkok.
Police have reportedly ruled out international terrorism and said they had detained some suspects.
Security is understood to have been tightened in the tourist areas and at airports in the south of the country.
Brant Smith, from Canberra in Australia and on holiday in Hua Hin, told the BBC that people in the resort were "rattled" and that there was tight security around his hotel.
More than a million Brits holiday in Thailand every year.
