BANGKOK - FLASH floods, several metres deep in places, have swept through a major city in southern Thailand, stranding about 100,000 residents, officials said on Tuesday.

Heavy flooding has already killed more than 100 people in Thailand since October 10, mainly in central and eastern areas, and with the disaster spreading there are fears of more casualties.

Rising waters began to inundate Hat Yai city in Songkhla province late on Monday after days of heavy downpours, cutting power and affecting tens of thousands of people.

'Eighty per cent of Hat Yai is under flood water and 30,000 households with 100,000 residents are stranded in their homes,' Hat Yai mayor Prai Pattano said on local television. 'At the critical point the water is three to four metres deep,' he said.

The authorities estimate that almost six million people have been affected, with homes submerged and farmland or cattle destroyed. Prime Minister Abhisit Vejjajiva described the floods as 'a huge natural calamity'.

'I'm very concerned, especially about Songkhla province where all road access is cut by the floods,' he said. A hospital in the region was forced to evacuate patients on Monday after the area was hit by flash floods. In total 104 people, including three foreigners, have died in the disaster, which has affected dozens of provinces around the country, although the waters have receded in some areas.

Thai floods strand thousands