Police in riot gear have been called in to divide two groups of protesters outside Belfast City Hall.
Several hundred people are attending an anti-racism demonstration, while a smaller group have been at a UK Freedom March protest.
Smoke bombs were thrown during the lunchtime rallies. There was a loud bang from one of the devices.
One of the UK Freedom March posters is in support of Tommy Robinson, a former member of the English Defence League.
He is serving a prison sentence for contempt of court.
Both protests are expected to disperse shortly.