BOCHUM, GERMANY (DPA) - Prison authorities are conducting a manhunt after a Serbian jailed for robbery with violence in Germany vaulted to freedom over a five-metre prison wall, a spokeswoman for the prison in western city of Bochum said on Friday (Aug 16).

The 42-year-old man, who worked in the prison's gymnastics hall, made his escape on Thursday evening using a metal device he had secretly made.

The 1.7m tall escapee, who had been sentenced to prison until 2021, is reported to be extremely fit as a result of his workouts in the gym.

Five watchtowers at the JVA prison were not staffed as a result of work to remove asbestos, spokeswoman Candida Tunkel said. She added that there was no camera surveillance in the area concerned.

According to Tunkel, the man used his work in the gym to make a construction for scaling the wall, making use of parts of a metal frame used to support gymnastics mats and bolting them together.

As two groups of prisoners were exercising in the hall under guard, he said he was going for a shower. He used the opportunity to clamber through a skylight onto a roof and ran to a sports field where he drew his construction out of a container and used it to ascend the wall.

He used a plastic mat to protect himself from barbed wire on the wall.

"The man did not draw attention to himself during his time in prison and always conformed to the rules," Tunkel said.

Police immediately deployed tracker dogs and a helicopter. They published photographs of the man, who has shoulder-length brown hair and tattoos. They said he should not be approached.