At least four persons were killed and several others injured when supporters of Pakistan Muslim League-Qaid-e-Azam and Pakistan Muslim League-Nawaz exchanged heavy fire near the garrison city of Rawalpindi on Thursday as former Pakistan prime minister and PML-N chief Nawaz Sharif was addressing meetings in the area.

A group of PML-Q workers reportedly opened fire on PML-N supporters who were gathering about three kilometres from the airport in Rawalpindi for a meeting to be addressed by Sharif.

Television channels reported the two sides used small arms and AK-47 assault rifles in the intense gun battle, which caused chaos and panic in the area. The firing continued for over 30 minutes.

This was the first major incident of violence between supporters of rival parties in the campaign for Pakistan's January 8 general election.

Sharif's motorcade was immediately stopped on the Islamabad highway by senior PML-N leaders to ensure his security.

TV channels reported that police forces in the area withdrew from their positions because of the heavy exchange of fire by the two groups.

Police officials said the trouble erupted when some supporters of a local PML-Q candidate objected to PML-N men putting up posters in the area.

PML-N leaders also accused the PML-Q workers of harassing their party's supporters.