On Saturday night, police said riot officers continued to deal with disorder in the Newtownards Road, Albertbridge Road, Castlereagh Street and Templemore Avenue areas on the third consecutive day of violence in the east of the city.
A number of cars and barricades have been set on fire, while petrol bombs fireworks and bricks have been thrown at police.
Water cannon has been deployed against loyalist rioters and three AEP rounds have been fired by officers during the trouble.
"Police came under sustained attack from crowds of more than 100 people throwing petrol bombs, fireworks, bricks and other masonry," a PSNI spokesman said on Saturday night.
"One officer has been injured but didn't require hospital treatment."
"A number of arrests have been made."
There were also reports of public disorder in the Ballymena area. Police said Larne Road Link was closed from Pennybridge Roundabout to the Bog Road on Saturday night.
Earlier a man, aged 38, was arrested on suspicion of attempted murder, following reports of gunfire aimed at police lines on the Newtownards Road.
It is understood the PSNI helicopter was used to prompt the arrest.
Two other men were also detained during the afternoon violence.
One was charged with a number of public order offences and appeared before a special sitting of Belfast Magistrates' Court on Saturday night.
It came after police said they were attacked from a 100-strong loyalist crowd, who hurled bricks and fireworks at officers on Saturday afternoon. Water cannon was also used against rioters.
The trouble in Belfast began when hundreds of loyalist demonstrators returning from City Hall came under attack from missiles which were thrown from the nearby nationalist Short Strand area.
Earlier, up to 1,000 loyalists took part in a protest march in Belfast city centre forcing road closures and disrupting traffic and trade in the area.
The city centre protest passed off without incident. It was the latest in a series of demonstrations which have been staged throughout Northern Ireland after Belfast councillors voted to only fly the Union Flag from City Hall on designated days.
East Belfast MP Naomi Long has repeated her call for protests to end, describing reports that shots had been fired as "deeply disturbing."
The Alliance politician said it was further proof the ongoing protests were becoming inextricably linked with violence.
"This latest rioting, and chilling reports of shots being fired, mark a new low and must be unequivocally condemned," she said.
"Violence has become more orchestrated. Those who claim leadership of the protests need to bring them to an end so we can discuss any grievances they feel they have in a democratic and peaceful manner," she added.
East Belfast Councillor Niall Ó Donnghaile said: "It is important the PSNI act to ensure that attacks on isolated catholic communities like the Short Strand masked under the guise of flag protests are brought to an immediate end.
"There has been some good work done by the PSNI in keeping unionist rioters away from this community but significant mistakes have been made in facilitating illegal protests and marches in East Belfast," the former Sinn Féin Lord Mayor added.
SDLP policing spokesperson Conall McDevitt said: "Those organising these protests on social media must bear full responsibility for the violence that has ensued and must be fully held to account for violence that is continuing to take place."
Meanwhile, the Chairman of the Police Federation for Northern Ireland told UTV that the PSNI was being stretched to the limit by the geographical spread of the often sporadic violence - and also the "very severe" threat from dissident republicans.
Terry Spence said he believed the UVF orchestrated violence in the east of the city.
He added that people should now realise the protests have been hijacked by paramilitaries - and should stay away from them.
Mr Spence said the police force was under resourced and needed additional man power.
On Friday night, nine officers were injured in street violence in the Greater Belfast area. The previous night, 10 officers also sustained injuries.
First Minister Peter Robinson has strongly condemned the rioting.
"The violence and destruction visited on the PSNI is a disgrace, criminally wrong and cannot be justified," the DUP leader said.