BRUSSELS - A notorious criminal escaped from a Belgian prison Sunday after a helicopter crash-landed inside the prison grounds, the local public prosecutor said.

Serial escapee Nordine Ben Allal managed to flee in a car after the hijacked helicopter crash caused confusion and threw up billows of smoke in the grounds of the Ittre prison some 40 kilometres (25 miles) south of the Belgian capital, the Nivelles region prosecutor Jean-Claude Elslander told reporters at the prison south of Brussels.

One inmate was injured when the helicopter landed.

An earlier report said that two prisoners had escaped, however local officials said the second man was an accomplice who arrived in the helicopter.

According to initial police enquiries, the daring prison raid began in late afternoon when four armed and hooded men burst into the premises of a nearby enterprise where a prototype helicopter was being worked on.

The assailants seized the mechanics, allowing them to leave after hijacking the aircraft and forcing the pilot to fly it into the prison grounds.

The helicopter crash-landed, injuring one inmate, who may have been attempting to board.

Ben Allal's accomplice aboard threw the convict a firearm and the pair escaped, briefly taking two prison guards hostage as they fled, while other prison warders were attending the injured man, according to the early reports.

They escaped in a waiting car which was later found abandoned nearby. "The presence of another vehicle is therefore possible," the prosecutor said.

A major search for Ben Allal was underway.

Ben Allal, who has a string of convictions for violent crime, has gained a reputation for escaping prisons, including in 2004 when two police officers were injured during an escape.