ReutersThe bus, carrying dozens of primary school age children, was returning from a trip north of BangkokThe 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.Transport Minister Suriyahe Juangroongruangkit said the bus was powered by “extremely risky” compressed natural gas.Getty ImagesDistraught loved ones of people killed in the tragedy visited the crash siteWitnesses 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.ReutersFirefighters remove a wrapped-up body from the bus”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. Getty ImagesRescuers pulled children’s bodies from the charred wreckageThe driver has fled the site of the crash but authorities are confident he will be tracked down, according to Thailand’s Interior Minister Anutin Charnvirakul.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.