Nearly two dozen students and teachers in Thailand are feared dead after a school bus was engulfed in flames on Tuesday while traveling for a field trip on Tuesday, officials said.

The bus was traveling from central Uthai Thani province to Ayutthaya and Nonthaburi provinces when the fire occurred on the outskirts of the capital Bangkok, Transport Minister Suriya Juangroongruangkit told reporters at the scene.

Images captured at the scene show the flames engulfing the scorched bus as plumes of black smoke billowed into the air.

"Teachers told us that the fire ignited very quickly," acting police chief Kittirat Phanphet told reporters. "From speaking to witnesses, we believe the explosion was caused by a spark from the tire that lit the gas cylinder that was powering the vehicle."

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He added that some students escaped through windows as the fire burned.

Piyalak Thinkaew, a rescuer of the Ruamkatanyu Foundation, told reporters that 23 passengers – three teachers and 20 students – onboard the bus were missing and feared dead. It was earlier believed that 25 were feared dead, but Thinkaew said that two more survivors had been found.

The students on the bus were reported to be in elementary and junior high school.

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Juangroongruangkit said 16 students and three teachers were hospitalized and receiving treatment. Their conditions were unclear.

Phanphet said that an investigation is underway.

Prime Minister Paetongtarn Shinawatra offered her condolences in a post on social media platform X, saying the government would take care of medical expenses and compensate the victims’ families.

"As a mother, I would like to express my deepest condolences to the families," she wrote.

The Associated Press contributed to this report.