"I'm afraid of getting heatstroke," the 51-year-old told AFP as the mercury hit 37 degrees Celsius (99 degrees Fahrenheit), with humidity pushing the "real feel" to a sticky 43C (109F).

Large swathes of Southeast Asia are struggling through a heatwave that has broken temperature records and forced millions of children to stay home as schools close across the region.

Experts say climate change makes heatwaves more frequent, longer and more intense, while the El Nino phenomenon is also driving this year's exceptionally warm weather.

Among those hit hardest are workers whose jobs require them to be outdoors all day, such as the motorbike drivers who deliver food and offer taxi rides through Bangkok's traffic-choked streets.

"My self-protection is to drink more water, so I can carry myself and not pass out," Suriyan said.

"In hot weather like this, I drink whenever I park my bike."

The air-conditioned malls from where he collects his deliveries offer some respite, but he also worries the rapid change in temperature risks making him sick.

Isara Sangmol is one of the city's legion of "win motosai" -- motorbike taxi drivers -- and has been on the job since he was 17.

These days he drinks four or five bottles of water a day to stay hydrated -- double his normal intake.

"We need to get enough sleep to work, otherwise the heat would affect our body and our health," the 48-year-old told AFP as he sipped water from a tumbler.

He waits for customers in the early afternoon at a motorbike stand that offers some shade.

"If it gets too hot for me, I can take off my orange 'win' jacket (worn by motorbike taxi drivers) and go inside the mall to cool down," he said.

He switched up his clothing for lighter fabrics that are more breathable, but driving a motorbike means he needs to wear long trousers and proper shoes.

Seksith Prasertpong has been delivering food for the Line Man app for the past two years and said the heat "makes my job harder".

"I have to wash my face more often, go to the toilet, and drink cold water regularly," the 38-year-old told AFP during a break.

Though the heat eases later in the day, Seksith said changing his working hours is not an option.

"Our rate is low. But the more we work, the more we earn," he said.

He would like to see incentives for drivers during hot weather, as is currently the case during heavy downpours when delivery rates are increased.

Suriyan also thinks rates ought to be raised to reflect the difficulties of the job.

Even in the heat, "riders like me still have to work because we need money to live our daily life... especially now when everything is getting more and more expensive," he said.

"I don't think there's any option to help us, because we have to be outside."