A theme park ride collapsed Tuesday in a city in western Sweden, injuring at least 18 people, officials said.

Two people were seriously hurt when the swinging Rainbow ride collapsed at the Liseberg theme park in Goteborg, SOS Alarm rescue service spokeswoman Monica Grandin said.

She said the numbers were still not definitive, but initial information that 40 people had been injured was incorrect.

Around 25 ambulances had been sent to the scene, she said. The ride was full when the accident occurred, Grandin said.

"Of course it is children who go on these rides, but I can't say how many" of the injured were children, she said.

The Liseberg manager on duty, Peter Andersson, said it appeared the accident was caused by a malfunctioning ball bearing.

Andersson said the attraction had been through a security checkup in the spring and no faults were found.

The Rainbow is a spinning arm with a seating compartment on one end.

Liseberg is a popular tourist destination in Sweden and the biggest fun fair park in the Nordic region, with more than 30 different rides.