Belgian police have detained three men after they took a hostage in an apartment building in the western city of Ghent.

It is still unclear why the men took the hostage - who was released unharmed - but it was not an act of terror, federal police spokeswoman Annemie Serlippens said.

"There appears to be nothing political," she said.

Four armed men had been reported entering the apartment block early today in the working-class area, prompting police to set up a big security operation to keep bystanders away.

After several hours, at least two men left the building with their hands up. It was unclear how the third man came out or whether police were still looking for more suspects.

Local media reported a previous hostage incident in Ghent two months ago that was linked to extortion.