UPDATE: all riders have now been freed and the family of the four seriously injured teenagers have been informed.

FOUR teenagers have been serio injured after two carriages of The Smiler rollercoaster collided at Alton Towers Resort.

Two teenage boys and two teenager girls received leg injuries after the carriage they were on collided with a stationary carriage at just after 2pm.

Once they have been released from the ride by emergency crews, all four seriously injured teenagers will be airlifted to major trauma centres at University Hospital Coventry and Warwickshire and Royal Stoke University Hospital for further emergency treatment

In total, sixteen people on board the 14-loop rollercoaster at Alton Tower Resort in Staffordshire required triage and it is hoped 12 will be discharged at the scene.

A platform has been built so the emergency services can reach the rollercoaster's riders who are approximately 25 feet up in the air at an angle of about 45 degrees.

A 999 emergency called from the theme park was received by West Midlands Ambulance Service at 2.09pm reporting that a carriage of The Smiler had collided with a stationary carriage.

Community first responders based at the theme park were first on the scene.

Four Midlands Air Ambulances are at the scene as well as four ambulances, a MERIT trauma doctor and three BASICS doctors, paramedics from the Trusts Hazardous Area Response Team (HART) and several senior paramedic managers are currently in attendance.

A West Midlands Ambulance Service spokeswoman said: “Of the 16 occupants on board the ride, two teenage boys and two teenage girls, have sustained serious leg injuries.

“A platform has been build up in order for emergency services to reach the occupants on the ride who are approximately 25 feet up in the air at an angle of about 45 degrees.

“Our HART paramedics, doctors, Staffordshire Fire and Rescue Service and Alton Towers’ rope rescue staff are working at height to carefully release and treat the four seriously injured teenagers.

"The 12 other occupants on the ride are said to have suffered minor injuries and it’s hoped that they will be discharged from the scene.

“Once released from the ride, all four seriously injured teenagers will be airlifted to major trauma centres at University Hospital Coventry and Warwickshire and Royal Stoke University Hospital for further emergency treatment.”

Alton Towers has set up a helpline for worried relatives: 0800 230 0770.