A roller coaster collision at a British amusement park has left four people seriously injured, according to an ambulance service.

West Midlands Ambulance Service says a car on the Smiler ride that was carrying 16 people at the Alton Towers amusement park collided with a stationary car on Tuesday afternoon.

The service says four of the people onboard "reported serious injuries."

It says paramedics, four ambulances and an air ambulance carrying a trauma doctor are on the scene.

The Smiler is billed as the world's first roller coaster with 14 loops. It opened in May 2013, two months later than scheduled, after a series of glitches.

Alton Towers, 150 miles (240 kilometers) north of London, is one of Britain's most popular tourist attractions.