Violence flared in Belfast and businesses were attacked after an anti-immigration protest moved through the city.
Police mounted a significant security operation during a lengthy confrontation between the protesters and those taking part in an anti-racist rally at the City Hall during which fireworks and other missiles were thrown.
The anti-Islamic demonstration then travelled towards the university area of the city where there were clashes with residents of the Lower Ormeau area.
Police said they were treating reports of criminal damage as hate crimes and said two arrests had been made.
Police Service of Northern Ireland (PSNI) vehicles and officers in riot gear were separating the groups.
Officers were seen arresting one man, who was taken away in a PSNI car.
Hundreds of people turned up for an anti-racist counter-protest in the heart of the city centre after social media calls for an anti-immigration demonstration in the city in the wake of the murders of three young children in Southport.
There were speeches and anti-Nazi chanting at the rally, which featured trade union banners and Palestinian flags.
Shortly after the rally began, a number of anti-Islamic protesters gathered across the road.
The group chanted “Islam out” and unfurled union flags.
There were also Irish Tricolours at the anti-Islamic protest as a delegation from Coolock, the scene of anti-immigrant protests in Dublin, arrived.
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The standoff between the two opposing groups became heated and police moved in to separate them.
A number of roads into Belfast have been closed “due to ongoing protest activity”, police said.
The PSNI said it is “aware of several planned protests across Northern Ireland today and will be in attendance to ensure the safety of everyone involved”.
Meanwhile, in Southport, England eight people were arrested and three police officers were taken to hospital for treatment following riots overnight.