At least 16 people were hospitalised in Thailand on Tuesday when a school bus carrying an estimated 44 students and teachers on a field trip caught fire on the outskirts of the capital Bangkok, the government said.

The status of the other passengers was not immediately clear and police did not immediately confirm if any of the passengers were killed.

Sixteen students and three teachers were sent to a hospital for treatment, Transport Minister Suriya Juangroongruangkit said, adding the causes of the incident were still be investigated.

Early images posted on social media and carried by local news outlets showed thick grey smoke pouring out of the bus, parts of which were still on fire.

The blaze was later extinguished. A Reuters photographer saw fire trucks, police and rescue vehicles parked around the blackened vehicle, with a cluster of firefighters at the entrance.

Prime Minister Paetongtarn Shinawatra said the students were on a field trip from the province of Uthai Thani, about 250 km (155 miles) north of the capital.

“As a mother, I would like to express my deepest condolences to the families,” she said in a social media post on X, without providing details.