Three shots were fired during the disturbances around the Short Strand area of east Belfast, which has seen its most serious rioting for several years.
The Press Association photographer, Niall Carson, who was covering the violence, suffered an injury to the leg and was taken to the Royal Victoria Hospital, where he was said to be in a stable condition.
A police spokeswoman said officers were dealing with "serious disorder" in the Lower Newtownards Road area of East Belfast.
She confirmed water cannon had been used and advised the media to stay away from the area for their own safety.
Dissident republicans have been responsible for a string of attacks on members of the police and army.
In April they killed Constable Ronan Kerr, 25, in an under-car booby trap bomb outside his home in Omagh, Co Tyrone.
There have been pitched battles between loyalists and republicans in the Lower Newtownards Road and Short Strand areas during the last two days. The police were targeted after they came between the two sides.
The Ulster Volunteer Force has been blamed by senior police for igniting trouble after a second night of serious rioting in Belfast.
Assistant Chief Constable Alistair Finlay said the loyalist paramilitary group started the violence.
Mr Finlay said: "The UVF in East Belfast started this - there was no sense of anyone trying to finish that.
"Their hands are upon this, whether by direction, by omission or commission."
A 20-year-old woman was arrested on a weapons charge during the rioting, which saw youths smashing police vehicles with sledgehammers and hurling petrol bombs.
A water cannon vehicle sustained a cracked windscreen and there were marks from live fire.
Several shots were fired and a Press Association photographer was shot in the right leg. He is recovering in hospital.
Police fired 66 baton rounds.
Mr Finlay said the attacks were less orchestrated than the previous night, when two people were injured by gunfire.
He appealed for parents to look after their children.
He refused to say whether the shots were fired from the nationalist Short Strand or the loyalist Newtownards Road but called for dialogue to discuss all issues behind the violence.
"Last night again we witnessed serious, sustained violence.
"Over two nights we have seen three people shot and injured, communities wrecked, houses and businesses damaged, lives put at serious risk.
"This has got to stop, it is a time for cool heads, for people to take a step back."