6 police officers hurt in N. Ireland violence, authorities say

(CNN) - Six police officers were hurt Monday in several areas of Belfast, Northern Ireland, in violence stemming from an annual Protestant holiday, authorities said.

The injuries occurred during "serious disorder" as a Protestant parade was set to pass through, Northern Ireland police said. Protesters opposed to the parade pelted officers with gasoline bombs, paint, fireworks, stones and bottles, authorities said, and at least one gunshot was fired at police. In turn, police used water cannons and fired plastic bullets.

The officers were injured in the Ardoyne, Londonderry and Rasharkin areas of northern Belfast.

The parade is a yearly event celebrating the "Twelfth" holiday, in which British Protestants celebrate victories over Irish Catholics. It proceeded quietly last year.

A peaceful protest against the parade took place earlier Monday, but the violence erupted about 4 p.m. (11 a.m. ET), police said. Officers were already in the area because of the earlier protest.

Sporadic outbreaks of violence continued Monday afternoon and evening. Authorities said they would maintain a presence there and monitor the situation.

No arrests were made Monday, but police said they were gathering evidence.

–CNN's Nicola Goulding contributed to this report.