Three more people were killed and dozens others injured across Egypt's Nile Delta cities in another spate of violence between supporters and opponents of beleaguered President Mohamed Morsi since Wednesday - two days before planned mass demonstrations against him.

A young man was shot dead and 30 others injured in clashes between the two rival camps in Sharqiya's Zagazig city on Thursday, Egypt's health ministry details.

The victims are members of the Muslim Brotherhood's Freedom and Justice Party (FJP).

Four of those injured have suffered gunshot injuries, says FJP Media Advisor Ahmed Gaber.

The party's Sharqiya headquarters was looted and set ablaze by members of the Rebel Campaign and the Constitution Party, according to Gaber. Police refused to do anything, fearing "engagement in politics," as he explained.

Two Islamist protesters injured in clashes in the Nile Delta city of Manoura two days ago have succumbed to their injuries, driving the death toll in that city to three.

Violence reportedly erupted on Wednesday after a group of opponents attacked a pro-Morsi rally.

Tension has been mounting across Egypt amid growing polarisation between President Morsi's Islamist backers and his opponents ahead of mass, nationwide rallies – mainly by secularist opposition – calling for his removal on Sunday.

Morsi backers, meanwhile, are bussing fellow supporters into Cairo on Friday for counter-demonstrations.

Deadly clashes also erupted across the Nile Delta provinces of Sharqiya, Gharbiya and Menoufiya on Thursday.

Gharbiya's Mahalla saw another flare-up of violence in Bishbeesh village. Pro- and anti-Morsi protests had several clashes until police later moved in to keep the warring sides apart.

A six-storey building, reportedly belonging to a supporter of the Muslim Brotherhood, the organisation which propelled Morsi to power last year, was set ablaze during the violence.

An electrical transformer was also set alight, plunging half of the city into complete darkness.

In the Nile Delta's Menoufiya governorate opposition supporters locked horns late on Wednesday with around three thousand pro-Morsi protesters in Shibin Al-Koum city.