A girl was rescued after being found fast asleep nearly 40m up on the arm of a crane, police said yesterday.

Emergency services were called to a building site in London after a passer-by spotted the 15-year-old sleepwalker curled up on top of a concrete counterweight high above the ground.

The unnamed teenager had climbed up the crane and walked across a narrow metal beam while fast asleep during the incident, which happened on June 25. It is believed that the teenager had walked out unnoticed from her home near the site in Dulwich, southeast London.

She was brought down in a hydraulic lift after a two-hour rescue operation. "Police and London Fire Brigade attended and the girl was brought down from the crane at around 4am," police said.

An expert from the London Sleep Centre, however, said he had handled more complicated cases. Irshaad Ebrahim told the Times that he had treated people who had driven cars and ridden horses while asleep.

One patient had even attempted to fly a helicopter. Sleepwalking affects one in 10 people at least once in their lives.