OSLO (AFP) - Three people were killed on Monday when a man armed with a knife hijacked a bus in western Norway, police said.

The suspected hijacker, a man in his 50s of foreign origin, has been arrested, police officer Joern Lasse Foerde Refsnes told the TV2 Nyhetskanalen news channel.

"For now, I have no information to indicate there was anyone else but the three victims" on the bus, he said.

The identity of the suspect, who was himself injured according to Norwegian media, as well as the motives for the attack were not immediately clear.

The man was overpowered by firefighters who rushed to the scene of what they initially believed was a traffic accident, police said.

The long-distance bus was on the route between the mountainous Valdres region, a popular area for skiing, and Oslo.

Nothing suggests that the alleged perpetrator and the victims knew each other, according to police.

A witness who was the first to arrive at the scene said he initially believed there had been an accident and rushed to help people inside the vehicle.

"The bus was on the side of the road, so we stopped our car and ran over," the witness told TV2 Nyhetskanalen, which identified himself only by his first name Leif.

He said he and another person tried to open the doors, but in vain.

"It was impossible to open the doors. Then we saw a dark-skinned person inside the bus. At first, we thought he was trying to get out but then saw he was moving around with a knife, and we realised that the situation was quite different," he said.

In 2003, on the same route between Valdres and Oslo, an Ethiopian killed the driver of a bus after murdering an asylum seeker in a local shelter.

He was sentenced to treatment in a psychiatric hospital.