Athens, Dec 30 (DPA) A bomb exploded outside a court in the Greek capital Athens Thursday after an anonymous warning call, a police source and witnesses said.

The device was planted on a motorbike parked in front of the building in the city centre, according to unofficial reports from the police.

Witnesses reported seeing burning cars and a cloud of smoke coming from the building.

There were no immediate reports of injuries. A witness told reporters that police evacuated the building before the explosion.

An unknown man allegedly called a television channel and a newspaper to warn of the bombing around 45 minutes before the explosion.

The courthouse was badly damaged in the blast and windows within a radius of almost 200 metres were broken.

The blast was heard across a large part of the Greek capital.