The mercury was forecast to hit 39C in the sprawling Thai capital, while the heat index rose above 52C, classed as "extremely dangerous" by city authorities.

The heat index is a measure of what the temperature feels like, taking humidity, wind speed and other factors into account.

"Warning: the heat index today is 'extremely dangerous'. Please avoid activities outdoors," the Bangkok city authority's environment department wrote in a Facebook post.

"The heat index is classed as extremely dangerous when it goes above 52 degrees Celsius."

April is typically the hottest and most humid time of the year in Thailand, but conditions this year have been exacerbated by the El Nino weather pattern.

The kingdom has sweltered through a heatwave this week, with a temperature of 44.2C recorded in the northern province of Lampang on Monday -- just shy of the all-time national record of 44.6C.

But for many who make their living on the streets of the city, staying indoors is not an option.

"I feel like almost fainting when I work outdoors these days but I don't have any choice, do I?" motorcycle taxi driver Boonsri Waenkaew told AFP.

Food hawker Buppha Nakhin, grilling meatballs at a street stall in downtown Bangkok, said she tried to stay in the shade.

"It's very hot. The hot weather this year is the most extreme," she told AFP.

"Sometimes I feel dizzy but (did) not faint yet."

The hot weather is expected to continue in the coming days, and the government has urged people to stay hydrated, apply sunscreen and exercise indoors to avoid heatstroke.

Global temperatures hit record highs last year, and the United Nations weather and climate agency said Tuesday that Asia was warming at a particularly rapid pace.

psk-tak/pdw/dhw

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