At least 31 people were injured, one seriously, after a roller coaster accident occurred early Thursday at the Legoland amusement park in Günzburg, Bavaria, Germany, local police said.

Two trains collided, one of them stopped. The second driver did not brake hard enough to avoid the accident “for an undetermined reason,” according to police.

ten children injured

Among the injured are ten children, a teenager and a 20-year-old, according to the same source. A total of sixteen people had to be hospitalized but no details were given about the condition of the seriously injured.

Three helicopters, firefighters and emergency services were quickly dispatched to the scene. The exact causes of the accident have not yet been determined.

Another roller coaster accident has already occurred last week in Germany, in the town of Klotten. A 57-year-old woman died after falling from the carousel. An investigation is ongoing.