Media reports said about 10 people had been injured in the collision between the towns of Hillerod and Kagerup, about 40 kilometers (25 miles) north of Copenhagen.
A police statement called it “a serious accident” but a police spokesman told AFP that all passengers had been evacuated from the trains.
“Two trains collided and the police and emergency services are mobilised in large numbers,” the statement said.
The alert was raised at 6:30 am (0430 GMT), according to police spokesman Tim Simonsen.
“It was a head-on collision and there are injuries among the passengers,” he told AFP, without giving details.
Denmark prides itself on its safety record, but a 2019 train crash left eight dead and 16 injured.
In August last year, an express train hit a farm truck on a crossing killing one person and injuring 27 people.
