OSLO -- Four people are in critical condition after two local trains collided head-on in Denmark on Thursday morning, Danish broadcaster TV 2 reported.

A total of 17 passengers were injured in the incident, which occurred on the rail line between Hillerod and Kagerup, about 50 km north of Copenhagen, according to the report.

A military helicopter and several ambulances and medical transport units were deployed to the scene. Police said the road section in the affected area has been closed and is expected to remain shut for an extended period.

The cause of the incident was not immediately clear.