Four armed men have entered an apartment in the western Belgian city of Ghent, and police have blocked off a wide perimeter around the area.

Police said Monday that two hours in it was still unclear what the intention was, and there was no information available either about the armed men who entered the apartment block or whether they had taken hostages.

By midmorning a big police operation had been set up in the working-class neighborhood to keep bystanders away from the scene.