A powerful cyclone has left a trail of destruction in Sri Lanka, with reports of at least 334 people dead, in the latest disaster to strike across Asia.

Homes and buildings were buried under mudslides in the aftermath of Cyclone Ditwah, and more heavy rain is predicted in coming days.

It comes as Indonesia, Thailand and Malaysia also count the deaths from unrelenting floods, with a combined toll of more than 600.

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

A flooded road after heavy rainfall in a suburb of Colombo, Sri Lanka. Photo: AAP

Across Asia, millions of people have been affected, losing homes and livelihoods and searching for missing loved ones.

Some residents of the flood-hit Indonesian island of Sumatra have resorted to stealing food and water to survive, authorities say.

The floods, which hit Indonesia almost a week ago, have killed 303 people — with the number expected to rise as more bodies are recovered — and displaced thousands.

The deluges triggered landslides, damaged roads, cut off parts of the island and downed communication lines.

The challenging weather conditions and the lack of heavy equipment also hampered rescue efforts.

Videos on social media showed people scrambling past crumbling barricades, flooded roads and broken glass to get their hands on food, medicine and fuel.

Some even waded through waist-deep floodwaters to reach damaged convenience stores.

North Sumatra Police first reported incidents on Saturday night, police spokesperson Ferry Walintukan said, adding regional police had been deployed to restore order.

“The looting happened before logistical aid arrived,” he said.

“[Residents] didn’t know that aid would come and were worried they would starve.”

Eleven helicopters were sent from Jakarta to affected areas on Sunday for logistics distribution operations, especially to places where land access was cut off, Cabinet Secretary Teddy Indra Wijaya said.

“But unpredictable weather often hampers aid operations,” he said.

The Cabinet Secretariat released footage of the military airdropping supplies to the affected areas.

In the village of North Tapanuli, survivors waved frantically to the helicopters carrying aid. Meanwhile, four navy ships docked at a port to support aid distribution.

Local villagers walk past cars in a flooded area of Hat Yai, Thailand. Photo: AAP

The disaster in Sri Lanka, with floods and horror mudslides, is considered its worst disaster since the 2004 Boxing Day tsunami.

Almost 148,000 people have been displaced from their homes and are housed in temporary shelters.

Sri Lanka has been battered by severe weather since last week.

Conditions worsened during the week, with heavy downpours that flooded homes, fields and roads and triggered landslides in the tea-growing central hill country.

Authorities say Cyclone Ditwah, which developed in the sea east of Sri Lanka, was forecast to move toward India’s southern coast.