Heat stroke is a real danger with "feels like" temperatures of around 50 degrees Celsius possible in the current humid conditions, the weather office warns.
The Meteorological Department said that on Tuesday feels-like temperatures peaked at 50.6°C in Trat, 48.1°C in Bangkok, 42.5°C in Krabi, 39.9°C in Tak and 38.7°C in Nakhon Ratchasima.
On Wednesday feels-like temperatures would reach 51.4°C in Chon Buri, 48.3°C in Phuket, 48.1°C in Bangkok, 39.6°C in Tak and 39.4°C in Buri Ram, according to the Met office.
During high humidity, people tend to feel hotter than it actually is because their sweat does not cool their bodies, the department said.
The Department of Health warned that such high feel-like temperatures could cause heat exhaustion and even heat stroke, especially among people who spend a lot of time outdoors.
Temperatures for official record-keeping purposes are taken in the shade. The highest recorded temperature in Thailand was 45.4°C, in Mae Sot in Tak on April 15 last year. It topped the previous record of 44.6°C set in Muang district of Mae Hong Son on April 28, 2016.