A chain of tropical storms and monsoonal rains has battered Southeast and South Asia, setting off landslides, flooding vast tracts and cutting off communities from Sumatra island's rainforests to the highland plantations of Sri Lanka.

At least 1,812 people have been killed in the natural disasters rolling across Sri Lanka, Indonesia, Malaysia, Thailand and Vietnam over the past two weeks.

Indonesia's president on Sunday vowed to step up aid, with demonstrators rallying after the country's death toll surpassed 900.

More than two million people in Sri Lanka -- nearly 10 percent of the population -- have been affected by last week's floods and landslides triggered by Cyclone Ditwah, the worst on the island this century.

The Disaster Management Centre (DMC) said monsoon storms were adding more rain and making hillsides unstable, including in the central mountainous region and the north-western midlands.

Helicopters and planes were being used on Sunday to supply communities cut off by landslides in the centre of the country.

The Sri Lanka Air Force said it had received a planeload of relief supplies from Myanmar on Sunday, the latest batch of foreign aid.

The government has confirmed 618 dead -- 464 from the lush tea-growing central region -- while 209 people remain unaccounted for.

The number of people in state-run camps had dropped to 100,000 from a peak of 225,000 as floodwaters receded across the island by Sunday, the DMC said.

More than 75,000 homes were damaged, including close to 5,000 that were completely destroyed, it added.

- 'Disaster tourism' -

In Indonesia, President Prabowo Subianto on Sunday flew back to Sumatra's hard-hit Aceh province, with a ministry saying his visit was "to ensure the acceleration of emergency response and recovery in affected areas".

The Indonesian government has so far shrugged off calls to declare a national disaster, which would free up resources and help government agencies coordinate their response. The toll in Indonesia on Sunday remained at 916 dead, with 274 still missing.

Prabowo will also "monitor the distribution of aid, the evacuation process of residents, and measures to reopen road access," the Ministry of the State Secretariat said.

"The government emphasises that the handling of the floods in Aceh is a national priority and all resources are being mobilised to expedite the recovery of community conditions," it added in a statement.

Speaking shortly after arriving in the capital Banda Aceh, Prabowo promised that "we will put all our efforts into this, and later we will repair all the bridges, hopefully within one or two weeks".

Many survivors said their greatest need remained clean drinking water.

Some victims accused the Indonesian leader and other officials of engaging in "disaster tourism" and failing to address the crisis.

"We see that, including Prabowo's visit in Bireuen today, it seems like a disaster tourism trip," said Syahrul, a 35-year-old protester in northern Aceh province.

"We don't need officials to just observe. We need their presence to address the issues faced by the community," Syahrul told AFP.

Protesters carried placards reading: "The Aceh disaster is not a tourist spot; it's not enough for Prabowo to just take a stroll."

In Sri Lanka, the government unveiled a major compensation package on Friday to rebuild homes and revive businesses wiped out by the natural disaster, which hit the island as it was emerging from its 2022 economic meltdown.

A senior official earlier said recovery and reconstruction might cost up to $7 billion.

The International Monetary Fund (IMF) said on Friday it was considering Sri Lanka's request for an additional $200 million to help with rebuilding.

The money is on top of the $347 million tranche due later this month, part of a four-year, $2.9 billion IMF bailout loan agreed in 2023.

President Anura Kumara Dissanayake told parliament on Friday that Sri Lanka's economy had made a significant recovery, but was not strong enough to withstand the latest shock alone.