Paul Sharkey lived through decades of sectarian violence between Protestant and Roman Catholic communities known as “the Troubles,” but thought that bloody phase of Northern Ireland’s history was over.

Then, on Wednesday evening, he heard a loud noise near his house on the Antrim Road in Glengormley, on the northwest edge of Belfast. When he looked out of his window, a burning van was hurtling toward his home.

“It was heading toward me — I was panicking,” Mr. Sharkey, 71, said.

An empty home opposite was also ablaze, he said, while young men with balaclavas covering their faces were “running all over the place like rats.”

The violence erupted after a brutal stabbing attack in Belfast on Monday, after which the authorities charged Hadi Alodid, a 30-year-old Sudanese refugee, with attempted murder. Graphic footage of the assault spread quickly online and was amplified by far-right activists, who called for protests and shared plans for roadblocks and locations for demonstrations.

On Tuesday night, violence broke out in parts of the city, with masked rioters setting fire to a bus, cars and garbage cans. Emergency responders had to escort immigrant families, including a parent with a 2-month old baby, from homes that had been set ablaze in one area of Belfast, the police said.