A suspected car bomb had detonated early on Friday in the city, injuring one man who had been taken to hospital, Belfast Police said.
"At this time we believe a device has exploded under a vehicle," said police spokesman Darrin Jones.
Emergency services were attending the scene and the condition of the man was unknown, police said.
The man was a prison officer, the Irish Independent newspaper cited security sources as saying.
Police were unable to confirm any of the injured party's details.
A peace deal signed in 1998 ended three decades of violence in Northern Ireland between groups who favour remaining British and those who favour unification with Ireland, but pockets of division and occasional violence remain.
Militants groups including the Real Irish Republican Army have carried out attacks, particularly in recent years, in a splinter of conflict remaining from the Anglo-Irish war.