A car bomb rocked the Administrative Court of Athens in Panormos area at around 08:21 a.m. local time (0621 GMT) on Thursday, but no injuries have been reported so far.
Police evacuated the building immediately after receiving a warning call at 07:38 a.m. (0538 GMT) but have yet to confirm that everyone had left safely.
The car, parked outside the central Athens court, was engulfed in flames after the explosion, causing thick black smoke that enveloped the whole area. A witness said the car was lifted three meters off the ground by the explosion.
The court building and nearby parked cars were extensively damaged.
The area has been cordoned off by police.