A roller coaster accident in Sweden’s oldest amusement park left one person dead and nine injured when the train was partially derailled.

Officials at Grona Lund Park said that several passengers on the Jetline rollercoaster were sent tumbling to the ground after the train’s front veered off the track. The cause of this is unknown.

Witnesses said that the train cars stopped 20 to 25 feet above the ground. However, they also reported that two to three people had fallen out of them, with one of those clinging to track.

The identity of the passenger who died is not known. The majority of the injured, which included three children, had been released as of Monday. The regional government reported that four adults were still hospitalized. Two of them are in serious, but not life-threatening conditions.

On Monday, the Swedish Accident Investigation Authority launched an investigation into how the roller-coaster train partially derailled. Separately the police launched a criminal probe into possible charges such as involuntary homicide, bodily harm, and danger to other people.

Officials expect that the park will be closed for at least a week.

GronaLund, located on an island in Stockholm’s center near the city centre, was opened in 1883. It is now one of Sweden’s most popular theme parks. According to the park, the 2,600-foot Jetline roller coaster was opened in 1988. It was renovated in 2000. The roller coaster has a height of up to 98 feet, and can reach speeds of up to 56 mph.