Four armed men have entered a flat in the Belgian city of Ghent and police have sealed off the surrounding area.
Unconfirmed reports suggested that the four had taken a man hostage and police urged residents to remain indoors for their own safety.
The men burst into the flat in the Dampoort area of the city, in northern Belgium.
Reporters at the scene said later that up to three people had given themselves up without violence.
But it was not yet clear whether they were suspects and whether the siege was continuing.
Local prosecutors said there was no indication of any link to terrorism or jihadist group Islamic State.
“This isn’t the same sort of incident as the events in Sydney,” spokeswoman Annemie Serlippens said.
The head of Ghent police Filip Rasschaert told De Standaard website that they were carrying out the operation carefully because of the potential involvement of a hostage.
Federal authorities were now in control of the siege, he said.