A teenage boy was airlifted to hospital after falling through the roof of an empty building in Ferrybridge.
Firefighters from Pontefract Station were alerted to the incident, off Fishergate, at around 5.20pm yesterday.
Watch commander Richard Beevers said they believe the boy had climbed a tree to the rear of the nearby Magnet Inn pub, giving him access to the roof.
He said: "He was walking across the roof and fell through a plastic skylight, about 20ft onto a concrete floor."
He said an ambulance and air ambulance were called and the 17-year-old boy was airlifted to Leeds General Infirmary with suspected pelvic injuries.
Watch commander Beevers said: "It was a corregated asbestos sheet roof. Asbestos is not very strong as it is but over time it becomes more and more brittle.
"I'd urge people to stay off any roofs in general - they aren't to be climbed upon and you don't know what these buildings could have inside."