The bodies of 20 children and three teachers have been recovered after a bus transporting school pupils crashed and caught fire outside Bangkok.

The bus was returning to the Thai capital after a school trip to the north of the country.

Videos 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.

The driver handed himself in to police 100km (61 miles) north of Bangkok, according to local media.

Footage taken shortly after the fatal crash showed the driver attempting to extinguish the fire but he reportedly fled the scene.

Witnesses say the bus crashed into the concrete barrier dividing the highway just north of Bangkok, after a front tyre burst.

The bus was quickly consumed by an intense fire, and many on board were unable to get out. The cause of the fire is still unknown.

Nineteen children and three teachers are reported to have survived, sixteen of whom are being treated in hospital for their injuries.

Transport Minister Suriyahe Juangroongruangkit said the bus was powered by “extremely risky” compressed natural gas.

“This is a very tragic incident,” Mr Suriyahe told reporters at the scene.

“The ministry must find a measure… if possible, for passenger vehicles like this to be banned from using this type of fuel because it’s extremely risky.”

Piyalak Thinkaew, who was leading the search, said it was hard to identify the bodies because they were so badly burnt.

“Some of the bodies we found were very, very small,” he told reporters at the scene, adding that the fire started at the front of the bus.

“The kids’ instinct was to escape to the back so the bodies were there,” he said.

Forensic police said of the 23 bodies found, eleven were male, seven female and a further five were unidentifiable.

The ages of the children on board remains unclear, but the school caters for pupils between three and 15 years old.

Thailand has one of the worst road safety records in the world, with unsafe vehicles and poor driving contributing to roughly 20,000 fatalities a year.

Thailand’s Deputy Prime Minister, Anutin Charnvirakul, said an investigation was underway. “We have to investigate the trace of driving from the tire marks, the burning trace, and CCTV footage,” he said.