Two teenagers are lucky to be alive after they crashed through a skylight in a school roof trying to retrieve a tennis ball.

Carrie Hamilton, 15, and Sean Kouvilirja, 14, suffered serious injuries when they plunged 15ft into a science laboratory.

Police officers feared the worst when they climbed up a drainpipe and peered through the shattered skylight.

The two friends were lying motionless on the classroom floor at the Holy Family RC School at Carlton, near Selby.

Carrie, who suffered spinal and head injuries, was surrounded by pools of blood.

She was taken to hospital where scans and X-rays revealed no permanent damage and she was discharged three days later.

Sean, who had a suspected broken arm and collarbone, was also allowed home after treatment.

Police said the pair could have lain injured in the classroom until the next morning but for Carrie's brother, Jason, 14, who was on the roof with them and raised the alarm.

The accident was a chilling echo of a recent incident when a teenager was critically injured after crashing through a skylight while skateboarding on a school roof near Catterick.

Yesterday Carrie's parents, police and North Yorkshire County Council education chiefs warned youngsters not to climb on to school roofs under any circumstances.

A county council spokesman said they had launched a full investigation into the Carlton school incident.

Selby police constable Scott Nixon, who was first on the scene, said: "They are both lucky to be alive.

"A lot of factors went in their favour. The caretaker lived on the premises and was able to quickly alert police and paramedics.

"Fortunately they also missed the sturdy laboratory benches on their way down. It was a potentially fatal accident."

PC Nixon said he was a good climber, but even he found it difficult to shimmy up the drainpipe and negotiate an overhang to get on to the roof. He said: "With long summer nights approaching, it's important that both kids and parents are aware of the dangers."

Carrie's father, John Hamilton, a caretaker at nearby Carlton Primary School, said: "We're just relieved they are both all right.

"It came as a tremendous shock when I walked into the classroom. Carrie's face was covered in blood and there were pools of blood on the floor.

"We full support the campaign to keep kids away from school roofs."