Hundreds of rioting youths attacked police who answered reports of a stolen vehicle being set on fire in central Belfast overnight.
Officers were pelted with stones and bottles at the Westlink, a stretch of dual carriageway running through the city.
Police had gone to the area when the vehicle crashed along the dual carriageway, but then came under attack from a mob gathered at a bonfire in the nearby Devonshire area.
More than 200 people, who were commemorating the people interned during the Troubles, were involved, police said.
No one was injured. The Westlink was closed for a time as officers attempted to disperse the crowds and traffic lights were still out of operation hours later.