At least 23 people died after a school bus carrying students and teachers on a field trip caught fire on the outskirts of Thailand's capital Bangkok, local police say.

Sixteen students and three teachers were hospitalised, Transport minister Suriya Jungrungreangkit said.

"Initial reports said there are 44 on board, 38 students and six teachers. As far as we know now, three teachers and 16 students got out," he told reporters.

"For those still missing, we are not clear yet."

Some of the children who survived suffered horrific burns to their faces, mouths and eyes, doctors treating them told local media.

Police are hunting the coach driver after he fled the scene, acting national police chief Kitrat Phanphet told reporters.

The bus was carrying students from Uthai Thani province when a tyre burst on a highway in a northern Bangkok suburb, sending the vehicle crashing into a barrier, a rescue worker said in footage broadcast on local TV.

The bus was running on compressed gas and the crash ignited its fuel tanks, the rescue worker said.

Video footage from the scene showed flames engulfing the bus as it burned under an overpass, with huge clouds of dense black smoke billowing into the sky.

Prime Minister Paetongtarn Shinawatra said there were fatalities and offered condolences to the victims' families.

"I have learned of the fire on a bus carrying students from Uthai Thani … resulting in deaths and injuries," Paetongtarn wrote on X.

"As a mother, I would like to express my deepest condolences to the families of the injured and deceased."

The blaze has been put out but rescue workers have had to wait for the bus to cool down before searching it for bodies, a rescue worker said.

An official investigation into the incident is underway.

Thailand has one of the worst road safety records in the world, with unsafe vehicles and poor driving contributing to the high annual death toll.

AFP/Reuters