The toll from floods and landslides rose to 19 in North Sumatra, which has been battered by heavy rain for days, with dozens still missing.

Road access to some areas has been cut off by debris, with communications and electricity down too, National Search and Rescue Agency official Emy Freezer told AFP.

Heavy rain in Aceh has also forced the evacuation of thousands of people.

"This flood is truly severe," said 47-year-old Ibnu Sina, whose home in Aceh's second city Lhokseumawe was inundated.

The region's main highway was now impassable, he told AFP, leaving the region "completely paralysed".

"The regional (governments) are overwhelmed," he said.

The same weather system has caused enormous flooding in southern Thailand, particularly in Hat Yai, near the border with Malaysia.

Entire districts were submerged by flooding that pushed desperate residents onto rooftops.

Authorities said on Wednesday that 33 people had been killed across seven southern provinces.

Floodwaters began to recede in Hat Yai on Thursday but Kamban Wongpanya, 67, said she was not able to return home yet.

"The water rose to the ceiling of the second floor," she told AFP, explaining that she had to be rescued by boat.

"The water inside my house has dropped by half, but there are still strong-flowing floodwaters on the road to my house. I can't return home yet."

Many residents lost homes and livelihoods in the floods, which began last week in Thailand.

The region is experiencing its annual monsoon season, but scientists have shown that climate change produces more intense bouts of rain because a warmer atmosphere holds more moisture.

Warmer oceans also fuel more intense and wetter storm systems.

Hat Yai shop owner Chayaphol Promkleng thought at first that his business would be spared because initial flooding was "only ankle-deep".

He returned the following day to find his shop "flooded to waist-deep level".

"There was nothing I could do. I left the shop to save my life."

Thailand's government announced a compensation package this week for affected families of around $280 per household.

But Chayaphol said he lost everything.

"I have to start from zero."

Across the border, Malaysia's Civil Defence forces used boats to evacuate elderly or frail residents trapped in homes in the town of Kangar in Perlis state.

Two people have been killed in flooding in Malaysia so far, with authorities warning more heavy rain was expected in coming days.

Ali Mat Isa told AFP he carried his bedridden wife up the stairs on Wednesday night as floodwaters rushed into their home.

"I couldn't move to the flood relief centre because of my wife's condition," he said as he was helped into a boat in waist-high, murky brown floodwaters.

"It rose fast. I only managed to move the electrical items. Everything else, I left behind."

The frequency of flooding has increased in northern Malaysia in recent years, with urbanisation, poor drainage systems and deforestation among the contributing factors, said Renard Siew, climate change adviser to the Kuala Lumpur-based Centre for Governance and Political Studies.

"So, in some ways, we are anticipating that things are only going to get worse from here on," he told AFP.

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