Thailand mobilised its only aircraft carrier as efforts to rescue thousands trapped on storm-swept holiday islands intensified on Wednesday after severe flooding across the south killed 15.

Victims were either swept away by the rising waters, or buried in mudslides as the unseasonably wet weather deluged the homes and businesses of around a million people in what should be one of the hottest months of the year.

Rising waters have choked off road and rail links to the southern region, while islands in the Gulf of Thailand and Andaman Sea were left isolated as ferries were cancelled.

Air connections have also been disrupted although flights began to run again on Wednesday to some areas.

Around 13,000 holidaymakers had been stranded on Koh Samui alone, said Bannasat Ruangjan, of the island's tourism association, who warned that food and fuel stocks could run low in the next few days if rain continued to hamper the flow of supplies.

"We advised tourists to stay in hotels and not to travel to the airport until the situation returns to normal, so far food and utilities are still adequate but I worry about stocks of diesel," he said.

Bangkok Airways said it expected to transport about 2,000 people in 19 flights from Samui to the Thai capital on Wednesday "as the weather is starting to clear".

Bad weather and a power blackout at Samui airport grounded over 50 flights on Monday and Tuesday.

Deputy prime minister Suthep Thaugsuban said the government had sent its only aircraft carrier to rescue around 1,000 people stuck on Koh Tao island.

The 14-year-old HTMS Chakri Naruebet has a displacement of 11,485 metric tons and can accommodate 10 helicopters.

"There are roughly one million people affected in many provinces. At first we thought the flood would last a day or two, but now it has already been one week," he told reporters.

According to the Thai interior ministry, there are 1,225 tourists stranded in Koh Tao and 1,100 in the Phangan islands in the Gulf of Thailand.

There were about 70 holidaymakers in the Similan islands and 55 in the Surin island chain off the west coast of Thailand. It did not mention Samui.

A government statement said four people were confirmed dead after a mudslide in the Khao Phanom district of Krabi province early Wednesday.

More than 40 people were admitted to hospital after the mudslip, which Thai media said completely destroyed two villages.

The flooding, which began in southern Thailand a week ago, has killed seven people in Nakhon Si Thammarat province, three along the coast in Surat Thani and one in neighbouring Phatthalung.

In all, 80 districts of eight provinces have been declared disaster areas by Thailand's disaster prevention and mitigation department.

Devastating flooding across Thailand late last year left more than 220 people dead, damaging the homes or livelihoods of an estimated 8.6 million people in 51 of the kingdom's 76 provinces.