In this file photo taken on August 21, 2020, empty taxi boats are seen along the beach in Koh Tao island in the Gulf of Thailand. (Photo: AFP)

Three more Thai islands opened to vaccinated foreign tourists on Thursday despite a nationwide surge in Covid-19 cases propelled by the Delta variant.

The islands -- Samui, Tao and Phangan -- welcomed visitors as part of the kingdom's push to revive its battered tourism industry.

Thailand launched its "sandbox" scheme on July 1, allowing vaccinated travellers to visit Phuket island. Tourists do not have to quarantine in a hotel but cannot leave Phuket for two weeks.

Under Thursday's expansion, tourists must stay at an approved hotel on Samui for a week and can leave their accommodation on day four.

They will have to produce a negative Covid-19 test before being allowed to venture to Tao or Phangan after their first week.

Prime Minister Prayut Chan-O-Cha said communication was important so tourists understood the conditions for the Phuket and Samui schemes differed.

"We hope Thailand's tourism industry recovers as soon as possible so the happiness returns to Thais," Prayut said during an opening ceremony, speaking remotely.

The leader has been in self-isolation for almost two weeks after coming into contact with a positive case during the Phuket scheme launch.

The rest of the country is struggling to rein in infections from the Delta variant, which authorities say now makes up nearly 80 percent of its caseload.

Virus hotspot Bangkok and nine provinces are under tightened restrictions, including a night-time curfew and a ban on gatherings of more than five people.

Thailand recorded almost 9,200 new infections and a record daily high of 98 deaths on Thursday.