A lone criminal has robbed a bank at the European Union Parliament and made off with an undisclosed sum.

Parliament spokesman Jaume Duch Guillot says the man showed staff at the in-house bank what looked like a gun and sped off as soon as he was given the money from a vault. No one was injured in the robbery.

He said the legislature is visited by some 15,000 people, including dignitaries and top level politicians, making it difficult to have foolproof security at all times. The sprawling EU complex covers several blocks in central Brussels.

Guillot said Thursday that the legislature is a "very open parliament and we prefer to still be a very open parliament."

Police were still looking for the robber.