The death toll from floods across large swathes of Southeast Asia rose to at least 321 on Friday, with authorities working to rescue stranded citizens, restore power and communications and coordinate recovery efforts as the waters began to recede.

Large parts of Indonesia, Malaysia and Thailand have been stricken by cyclone-fuelled torrential rain for a week, with a rare tropical storm forming in the Malacca Strait.

Another 46 people were killed by a cyclone in the South Asian island nation of Sri Lanka, authorities said.

'Running out of supplies and food'

On Indonesia's badly hit Sumatra island, 174 people were confirmed dead on Friday, Suharyanto, the head of Indonesia's disaster mitigation agency, said at a press briefing.

While the rain had stopped, 79 people were still missing and thousands of families have been displaced, he added.

Residents in Sumatra's Padang Pariaman region, where a total of 22 people died, had to cope with water levels at least 1 metre high, and had still not been reached by search-and-rescue personnel on Friday.

"We're running out of supplies and food," said Muhammad Rais, a 40-year-old resident who was forced to move to the second floor of his home on Thursday to escape the rapidly rising waters.

In the town of Batang Toru, in northern Sumatra, residents on Friday buried seven unclaimed victims in a mass grave. The decomposing bodies, wrapped in black plastic, were lifted from the back of a truck on to a wide plot of land as onlookers held their noses.

Communications remained down in some parts of the island, and authorities were working to restore power and clear roads that have been blocked by landslide debris, said Abdul Muhari, spokesman for Indonesia's national disaster mitigation agency.

Indonesia would continue to airlift aid and rescue personnel into stricken areas on Friday, he added.

Thailand death toll reaches 145, tourists evacuated

The Thai government said that 145 people had been killed by floods across eight southern provinces. It said a total of more than 3.5 million people had been affected.

In the southern city of Hat Yai, the hardest-hit part of Thailand, the rain had finally stopped on Friday, but residents were still ankle-deep in flood waters and many remained without electricity as they assessed the damage done to their property over the last week. One said he had "lost everything".

Some residents said they were spared the worst of the floods but were still suffering from their effects.

"It affects everything for us, in every way," said 52-year-old Somporn Petchtae. "My place wasn't flooded, but I was stuck like I was on an island because I couldn't go anywhere."

In neighbouring Malaysia, where two people have been confirmed dead, tropical storm Senyar made landfall at around midnight and has since weakened. Meteorological authorities are still bracing themselves for heavy rain and wind, and warned that rough seas could pose risks for small boats.

A total of 30,000 evacuees remain in shelters, down from more than 34,000 on Thursday.

Malaysia's foreign ministry said on Friday that it had already evacuated 1,459 Malaysian nationals stranded in more than 25 flood-hit hotels in Thailand, adding that it would work to rescue the remaining 300 still caught up in flood zones.