The death toll mounted to over 600 from floods and landslides caused by torrential rains across three countries in Southeast Asia, officials said on Sunday, as relief efforts for tens of thousands of displaced people continued over the weekend.

Indonesia, Malaysia and Thailand faced large-scale devastation after a rare tropical storm formed in the Malacca Strait fuelling heavy rains and wind gusts for a week. There were 435 dead in Indonesia, 170 in Thailand, and three deaths reported in Malaysia.

Rescue and relief officials in the Southeast Asian countries were still trying to get access to many flood-hit areas on Sunday even as flood waters receded and tens of thousands of people were evacuated across the three countries. Over 4 million people have been affected - nearly 3 million in southern Thailand and 1.1 million in western Indonesia, according to official statistics.

Separately, across the Bay of Bengal, another 153 people were killed by a cyclone in the island nation of Sri Lanka, authorities said, with 191 others missing and more than half a million affected nationwide.

Indonesia

The death toll surged in Indonesia to 435 on Sunday, up from 303 on Saturday, official data uploaded on a government website showed, as officials compiled reports of casualties and damage pouring in from the western island of Sumatra, where three provinces had been devastated by landslides and floods after the rains.

Many areas were cut off due to blocked roads, while damage to telecommunications infrastructure has hampered communication. Relief and rescue teams used helicopters to deliver aid to people in areas that could not be reached by road.

From a navy chopper flying over the isolated town of Palembayan in West Sumatra, a Reuters photographer saw large tracts of land and homes swept away by floodwaters. As the helicopter landed in a soccer field, dozens of people were already standing close by waiting for food.

There have been reports of people looting supply lines as they grow desperate for relief in other areas, officials said on Saturday.

"The water just rose up into the house and we were afraid, so we fled. Then we came back on Friday, and the house was gone, destroyed," Afrianti, 41, who only goes by one name, told Reuters in West Sumatra's Padang city.

She and her family of nine have made their own tent shelter beside the single wall that remains of their home.

"My home and business are gone, the shop is gone. Nothing remains. I can only live near this one remaining wall," she said.

According to official figures, 406 people were still reported missing and 213,000 displaced.

Thailand and Malaysia

Thailand's Ministry of Public Health reported the death toll from flooding in southern Thailand at 170, an increase of eight from Saturday, and 102 injuries. Songkhla Province had the highest number of fatalities at 131.

Hat Yai, the largest city in Songkhla, received 335 mm (13 inches) of rain last Friday, its highest single-day tally in 300 years, amid days of heavy downpours.

In neighbouring Malaysia, there are still about 18,700 people in evacuation centres, according to the country's national disaster management agency. Meteorological authorities lifted tropical storm and continuous rain warnings on Saturday, forecasting clear skies for most of the country.

Parts of the country were battered last week by heavy rain and wind. Malaysia's foreign ministry said it had evacuated over 6,200 Malaysian nationals stranded in Thailand.

On Sunday the ministry put out an advisory to its citizens living in Indonesia's West Sumatra to register with the local consulate for assistance. It said a 30-year-old Malaysian had been reported missing following a landslide in the area.