Clashes erupted on Wednesday night outside a Muslim Brotherhood conference in Desouk city in Kafr El-Sheikh governorate.
It is unclear who started the violence but tension was already high following the appointment of a new Islamist governor. Hundreds fought and threw stones outside the Ibrahim El-Desouky Mosque and in nearby side streets. Twenty-five people were injured in the violence, including one by birdshot pellet, Al-Ahram Arabic news website reported.
Unrest has taken place in several cities over President Mohamed Morsi's appointment on Sunday of seven Brotherhood members as regional governors. The move sparked anger over the Islamist group's perceived attempts to tighten its grip on the country's bureaucracy.
Brotherhood members are now governors of 11 of Egypt's 27 governorates.
In Gharbiya, members of the opposition Constitution Party and April 6 blocked the doors of the city council building on Thursday morning and began a sit-in to demand the new governor's resignation.
Dozens were injured over the past few days in Fayoum, Gharbiya governorate in clashes over the contentious new governor.
Dozens of people protesting outside the Daqahliya governor's office in Mansoura were reportedly attacked in the early hours of Thursday by unknown assailants wielding bladed weapons and bludgeons.
Members of the ultraconservative Salafist Front, meanwhile, claim they were assaulted by protesters in the vicinity of the governor's office in Daqahliya "because of their breads," Al-Ahram Arabic news website reported.
The health ministry said six people were injured on Wednesday during skirmishes in Mansoura between opponents and supporters of the newly appointed governor, Sobhi Attiya Younis, a member of the Brotherhood.
Violence erupted after hours of calm following earlier clashes. Demonstrators opposed to the governor had besieged Younis's office in an attempt to prevent him leaving the building.
Younis, 52, previously served as the Islamist group's spokesperson in the governorate.
President Morsi on Sunday named a member of Al-Gamaa Al-Islamiya as governor of Luxor. The group killed scores of Western tourists in the city in 1997. The group has since renounced terrorism and the governor claims never to have taken part in violence.