Four suspicious objects have been located at two addresses in the Lavinia Square and Ormeau Road area of south Belfast, and at two addresses in the Lepper Street and Victoria Parade area of north Belfast.
A number of homes have been evacuated with motorists advised to avoid these areas.
A PSNI spokesman said: “There are no further details at this stage.”
Sinn Féin councillor John Gormley condemned those responsible.
“I have been liaising with local residents and community groups to provide maximum support to those residents who have been evacuated from their homes,” he said.
“This was a senseless act and shows little regard for the community, our key workers, emergency services and health workers. It comes at a time when people are already dealing with very stressful situations.
“Those responsible for these suspect devices have absolutely nothing to offer our society. They must get off the back of the community of South Belfast and allow local residents to live in peace.
“I appeal for anyone with any information to bring it forward to the PSNI.”
