Loyalists and republicans fired shots near a sectarian interface, while petrol bombs and paint were hurled at Short Strand with some homes damaged.
Police confirmed some of the violence was orchestrated.
Sinn Fein blamed the Ulster Volunteer Force and unionists said attacks were launched from the grounds of a Catholic church during hours of trouble last night.
Assistant chief constable Alistair Finlay said: "It is probably the worst violence we have seen in that area for some considerable time."
Sinn Fein blamed scores of masked men, who a party representative said were wearing camouflage clothing and surgical gloves, for launching coordinated attacks on the republican Short Strand area.
Ulster Unionist Michael Copeland said he believed the violence followed attacks on Protestant-owned homes.
Belfast mayor Niall O Donnghaile, a councillor based in the Short Strand area, said a number of nationalist residents had been injured, including one man knocked unconscious when he was hit on the head with a brick. Police were also attacked during the disturbances and advised motorists to avoid the area.
Mr O Donnghaile said: "There is no doubt that this was unprovoked and was a carefully orchestrated and planned attack on the area.
"Homes have been attacked with petrol bombs and paint bombs, bricks, golf balls. I saw what happened."
But Mr Copeland said homes on the mainly Protestant Newtownards Road had been targeted.
"I would say it was several hundred involved in very serious, almost hand-to-hand fighting," he said.
Presbyterian minister the Rev Mervyn Gibson said houses on the Newtownards Road were being attacked from the Short Strand.
He said petrol bombs were coming from a nearby chapel's grounds, with homes under sustained attack for hours.
"It was a terrible sight, I thought those days were over," he added.