Japanese police officials say two Nepalese men killed in a traffic accident in northeastern Japan on Tuesday may have been trying to help their bus driver fix the vehicle's engine.

A large truck crashed into the bus on an expressway in Miyagi Prefecture on Tuesday night. Three people were killed, and one person was injured. The bus was parked on the shoulder of the road, as it was having engine trouble.

The third person killed was the female Japanese bus driver. The truck driver sustained serious head injuries. He is from Aomori Prefecture.

Police officials and a representative of an employment agency say the 40 passengers on the bus were all foreign students, who attend automotive repair schools or language schools in the city of Sendai. All the students -- 39 Nepalese and one Bangladeshi -- are in their 20s.

They were heading to a factory that belongs to the housing equipment maker Lixil. The factory is located in the adjacent prefecture of Iwate. The students work there part-time. They were going to assemble window frames.

All the passengers had reportedly gotten off the bus, after it started emitting smoke and having engine trouble.

The two Nepalese men are said to have been near the rear of the bus when the accident occurred.

Police quote multiple students as saying that the truck crashed into the bus about five or 10 minutes after the bus stopped.

Police are investigating further.