At least 115 people have been killed across South-East Asia after a week of record-breaking rain, flash flooding and landslides which metrologists say stemmed partly from a "rare" tropical cyclone.
In Thailand, at least 55 people died during severe floods from a week of heavy rain that has devastated nine southern provinces, its government said.
On Sumatra — an Indonesian island of 60 million people — a tropical cyclone unleashed deadly floods and landslides, leaving at least 60 people dead and a further 59 missing.
Meteorologists say current extremes of weather in South-East Asia could stem from the interaction of two active systems,Typhoon Koto in the Philippines and the formation of Cyclone Senyar in the Malacca Strait.
The Indonesian meteorology agency said the formation of Senyar in the Strait of Malacca was "rare".
"Indonesia's location near the equator theoretically makes it less prone to the formation or passage of tropical cyclones," the agency's Andri Ramdhani said.
However in the past five years, several tropical cyclones have moved towards Indonesia and had significant impacts, Mr Ramdhani said.
"Phenomena like Tropical Cyclone Senyar are relatively rare in the waters of the Malacca Strait, especially if they cross onto land," he said.
ABC meteorologist Tom Saunders said that while cyclones rarely develop or track near the equator, its "not unprecedented" to see weak systems briefly appear around a latitude of 5 degrees north or south.
The location of Cyclone Senyar was only a fraction south of 5 degrees latitude north, he said.
"As a general rule they don't form there however they can occasionally drift into these low latitudes after developing elsewhere, or even more rarely form just within 5 degrees."
Indonesia's meteorology agency urged local governments and communities in the affected areas to be prepared for "disasters".
This could include floods, coastal inundation, landslides, and fallen trees due to strong winds, they said.
In Indonesia, people were carried out of their homes through gushing water, reaching as high as a metre, and helped onto rubber boats in the teeming rain, video from the search and rescue agency showed.
Verified images from West Sumatra showed rescue teams carrying bodies through deep mud and cars displaced and on top of each other after being carried away by a tide of floodwater.
300-year rainfall record broken
Meanwhile, rescue teams in Thailand readied drones to deliver aid and helicopters dropped supplies to people marooned on rooftops as the death toll from its worst floods in years rose to 55.
The country's worst-hit city of Hat Yai received its highest single-day rainfall in 300 years — 335 millimetres.
Thailand has pushed relief efforts into high gear after the military brought in an aircraft carrier, 20 helicopters and convoys of trucks to deliver food, medicine and dinghies, and issued a public appeal for boats and jet skis to reach people stranded for days by waters up to 2 metres high.
After floodwaters receded in Hat Yai, authorities were optimistic that access could increase and basic services could be restored.
"Efforts to assist the public are continuing, but the flooding situation will be a long fight," Thai government spokesperson Siripong Angkasakulkiat said.
About 1 million households and more than 3 million people have been impacted by floods triggered by torrential rains in 12 southern provinces, the Department of Disaster Prevention and Mitigation said, with thousands of people huddling in evacuation centres.
Police said they were assisting 1,000 stranded foreigners, moving them to shelters at a university.
At an indoor basketball arena that was turned into an evacuation centre, 70-year-old Kritchawat Sothiananthakul described the inexorable rise of waters in his Hat Yai home, as he waited with his dog to be rescued.
"We had to climb down from the roof, get into the boat," he said.
"I needed to carry it and then get onto a truck … We had to leave everything because everything was submerged."
Army reinforcements arrive
Thailand's army engineering corps with specialist vehicles and 2,000 members of the civil defence corps arrived on Thursday in Hat Yai, where helicopters were delivering food to hospitals and victims still stuck on rooftops.
Aerial footage under grey skies showed miles of roads engulfed by brown water, with heavy-duty trucks crawling along wide thoroughfares past abandoned cars and trucks, as groups of people waded slowly through knee-deep water.
"I'm walking back to my grandmother because she hadn't had food for two or three days," said 18-year-old Natawat Chermmontri moments before diving into the water to swim across a road.
In neighbouring Malaysia, similar flooding in seven states has killed two people and forced more than 34,000 into shelters.
Container trucks were used to bring some Malaysians back over the border from Thailand, the foreign minister said, as smaller vehicles were unable to traverse the floodwaters.
Authorities said about 500 nationals were still stranded in Hat Yai, a city popular with Malaysian tourists.
At an evacuation centre in the state of Perlis, Gon Qasim said rising waters trapped her in her home in the middle of a paddy field.
"The water was like the ocean," the 73-year-old said.
On Thursday, authorities issued new warnings of a tropical storm until the weekend that could bring strong winds, rough seas and heavy, continuous rain affecting seven states in Malaysia.
Wires/ABC
