Swedish government investigators have launched a probe into a roller coaster accident that killed one person and injured nine at the country’s oldest amusement park.

The Gröna Lund park has been closed, and will remain closed for at least one week, after the accident Sunday, when a roller coaster train partially derailed, sending some passengers plunging to the ground.

One passenger died and nine were taken to Stockholm area hospitals. Most of the injured, including three children, were released by Monday. Four adults remained hospitalized, two of them in serious but not life-threatening condition, the regional government said.

Park officials said the front of the train derailed for unknown reasons and came to a halt between 6 and 8 meters above ground. Witnesses said two or three people fell out, one of whom managed to cling to the track.

Experts from the Swedish Accident Investigation Authority arrived Monday at Gröna Lund to investigate the accident on the Jetline roller coaster. The government agency is charged with investigating serious accidents with the aim of improving safety, rather than establish guilt.

Separately, police have launched a criminal investigation on possible charges of involuntary manslaughter, causing bodily harm and danger to others.

The 800-metre-long Jetline rollercoaster opened in 1988 and was renovated in 2000, according to Gröna Lund. It has a maximum height of 30 metres and a top speed of 90 kph.

Located on an island near Stockholm’s city center, Gröna Lund opened in 1883 and is one of Sweden’s most popular amusement parks.