"The man showed a gun, or something that like looked like a gun, the staff were afraid so they gave him the cash in the drawer and he escaped," European Parliament head spokesman Jaume Duch told this website.

Nobody was hurt, he added.

The bag used in the robbery was quickly recovered, another official said. But as of early evening, it was unclear whether the robber - reportedly wearing a wig and make up - remained on the loose inside the parliament or its vicinity.

"We are looking through the camera system now to see," said Mr Duch.

Several EU staff working in the large PHS office block, which contains the parliament's plenary chamber, were unaware of the drama. Others closer to the scene of the crime were alarmed by the heavy police presence, including helicopters.

The PHS building often plays host to VIPs, including heads of state, with former Soviet leader Mikhail Gorbachev attending an international water conference only two floors above at the time of the assault.

But the European Parliament has a low profile security presence compared to the European Commission and European Council complexes.

"It is not known whether the gun involved was real or fake," said the parliament spokesman. "Of course if it was a fake, it would be very difficult to prevent this sort of thing."

"We can never guarantee 100 percent security," he explained. "But this is the European Parliament and as such must remain a public building open and accessible to European citizens."

With additional reporting by Leigh Phillips.