Heavy monsoon rain overwhelmed swaths of Indonesia, Thailand and Malaysia this week, leaving thousands of people stranded without shelter or critical supplies.

At least two areas of Indonesia's worst-affected Sumatra island were still unreachable on Sunday, and authorities said they had deployed two warships from Jakarta to deliver aid.

Central Tapanuli and Sibolga city "require full attention due to being isolated", National Disaster agency head Suharyanto said in a statement, adding that the ships were expected in Sibolga on Monday.

The death toll in Indonesia rose to 442, while 402 were still missing, according to a tally published on Sunday by the disaster authority.

It said at least 646 people had been injured.

In Sungai Nyalo village, about 100 kilometres (62 miles) from West Sumatra's capital Padang, floodwaters had mostly receded on Sunday, leaving homes, vehicles and crops coated in thick grey mud.

Authorities had not yet begun clearing roads, residents told AFP, and no outside assistance had arrived.

"Most villagers chose to stay; they didn't want to leave their houses behind," said Idris, 55, who, like many Indonesians, goes by one name.

Across the island towards the north coast, an endangered Sumatran elephant lay buried in thick mud and debris near damaged buildings in Meureudu town.

- Public criticism -

In Thailand, where at least 162 people were killed in one of the worst floods in a decade, authorities continued to deliver aid and clear the damage.

Relief measures rolled out by the Thai government include compensation of up to two million baht ($62,000) for households that lost family members.

However, there has been growing public criticism of Thailand's flood response, and two local officials have been suspended over their alleged failures.

Two people were killed in Malaysia after floods left stretches of northern Perlis state underwater.

The annual monsoon season, typically between June and September, often brings heavy rain, triggering landslides and flash floods.

A tropical storm has exacerbated conditions, and the tolls in Indonesia and Thailand rank among the highest in floods in those countries in recent years.

Climate change has affected storm patterns, including the duration and intensity of the season, leading to heavier rainfall, flash flooding and stronger wind gusts.