April 23 (UPI) -- Two passenger trains crashed head-on in Denmark on Thursday leaving 18 injured, five of them critically, law enforcement officials said.

The trains collided at 6:29 a.m. CEST, traveling on a line that connects Hillerød and Kagerup in the North Zealand region of northeast Denmark. Hillerød is about 19 miles from Copenhagen. There were 37 people aboard. North Zealand police said the trains were traveling fast, but the exact speed wasn't known.

No cause of the crash has been determined, said Tim Ole Simonsen of the Greater Copenhagen Fire Department, but he told Danish TV that all the injured were taken to the hospital by either ambulance or air.

"I am deeply shaken and shocked, and my thoughts are with all those involved," Gribskov Mayor Trine Egetved posted on Facebook. "The local track is used by many Gribskov citizens, employees and pupils. Emergency services are working at full pressure, and we are trying from the central team to get an overview of what has happened more accurately and make sure that everyone gets the help they need."

Fire and rescue service leader Christoffer Buhl Martekilde told reporters, "The two trains collided head-on, causing large damage to them and sending broken glass flying everywhere."