Story highlights All but three of the victims were children

Only two students aboard survived, and they are in critical condition

(CNN) A school bus full of students swerved off a steep road in Tanzania on Saturday morning and fell into a ravine, killing 36 people -- 33 of them children, authorities said.

The fatal crash happened in city of Arusha in Tanzania's northern Karatu District, on the edge of the Ngorongoro Conservation Area.

"The place where it happened is a hill, with a steep slope, and it was raining when the accident happened," Aruba Police Commander Charles Mkumbo said.

Mkumbo added investigators were still trying to determine exactly what caused the bus to leave the road. "We don't know if the driver was new or if there was a mechanical defect," he said.

The bus driver and two teachers on board were also killed in the crash. Two of the students survived but were critically injured.

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