OSLO, Feb. 24 (Xinhua) -- One person was killed and two others were critically injured and hospitalized after coming in contact with a power source at a train tunnel's side track in Norway's capital city Oslo. public broadcaster NRK reported Sunday.

It was still unknown why the people were inside the tunnel, according to Tore Barstad, operations leader of the Oslo police.

"The two people who were first taken to hospital were able to communicate with. They told us that there was a third person inside the tunnel," he said.

The police then entered the tunnel and took out the third person who was declared dead.

The tunnel is located in the area at Filipstad in central Oslo and the side track is mainly used to turn trains.

In these areas, there is a high-voltage system with a voltage of 15,000 volts.

"It is confirmed that it has been unauthorized presence of people inside a small tunnel at Filipstad. Based on what we know, they have been in an area that is not intended for regular traffic," Harry Korslund, press officer of railway network agency Bane Nor, told news agency NTB.

No people were left in the tunnel and the accident had no consequences for the train traffic in the area, the report said.