Two trains have collided head-on on a level crossing north west of Copenhagen, leaving five people critically hurt and 13 others with less serious injuries, medical officials say.

The trains were travelling early on Thursday on a line linking the towns of Hillerød and Kagerup in the North Zealand area of north-east Denmark, with a total of 37 people on board, according to police.

Tim Ole Simonsen of the Greater Copenhagen fire department was unable to say what led to the crash but told Danish TV that all the injured had been taken to hospital by air or by ambulance.

Local mayor Trine Egetved said she was deeply shaken by the accident.

Public broadcaster DR showed images of two yellow and grey trains, both with visible damage to the front, facing each other in a wooded area.

Officials said the trains collided at 06:29 local time (05:29 BST) on Thursday and fire and rescue teams were alerted immediately.

Egetved, who is mayor of the Gribskov municipality, said those with critical injuries had been flown to the National Hospital in Copenhagen.

"The local track is used by many Gribskov residents, workers and students," she wrote on Facebook.

She told public broadcaster DR that it was shocking that two trains could collide head-on "and we must ensure it never happens again".

In a statement to government-owned station TV2, Prime Minister Mette Frederiksen said she was "very concerned by the terrible train accident".

Denmark's Accident Investigation Board arrived at the scene during the morning and Inspector Morten Pedersen of North Zealand police said they would be working together to find out what had happened.

Pedersen told reporters it was far too early to know the cause of the crash.

The board's railway unit manager, Klaus Jensen, told broadcaster TV2 investigators are looking at "all hypotheses", including "a failure in the signalling system, or whether there may have been a failure due to human factors".

Claus Pedersson, safety director at Lokaltog - which operates the train line - told public broadcaster DR that several members of staff have been injured.

He described the collision as "one of the worst we can imagine in the railway industry", adding that "right now we are collecting data" to understand the causes of the incident.

"We see accidents like this happen from time to time, and the most important thing is that we learn from it," he added.

In a separate interview with broadcaster TV2, Pedersson said initial reports suggest one of the train drivers pulled the brakes and then helped evacuate passengers.

He also reassured passengers, telling them "very competent" people drive the trains and monitor them.

Rail accidents are rare in Denmark and one expert suggested one of the train drivers had ended up on the wrong line by over-riding a stop signal as the train left a local station. The Gribskov line is not thought to have been updated with an automated safety system.