The device described by the PSNI as viable was left on grass at the bottom of the Lisburn Road, close to Bradbury Place around 11pm on Friday night.
"This was a viable device which was capable of causing death or serious injury and I would appeal to the community for information about the people who left this deadly device in the heart of our city," Inspector King from the PSNI said.
A number local residents took shelter at a community centre in Sandy Row.
Several businesses in the area also had to be evacuated.
South Belfast MP Alasdair McDonnell branded the disruption to trade as "grossly irresponsible".
"Businesses in Belfast, and in Bradbury Place where many of bars and restaurants are located, are fighting hard against the current economic tide," the SDLP politician said.
"Many workers had to wait several hours this morning before they could get to their place of work - that's unacceptable.
"I condemn this incident, those responsible have no role to play in this society as long as they continue on this path."
The alert ended just before 11am on Saturday.
All roads affected by the security operation have been re-opened.