Violent confrontations erupted in Alexandria, Smouha district, after a host of hooligans tried to break into the security directorate building late on Friday.
An unnamed security source said Central Security Forces (CSF), along with the security directorate guard and civilians, formed battalions to defend the building against the attacks.
The assailants threw rocks at the building in Egypt's second largest city before police forces replied by firing tear gas canisters. Hundreds were reportedly injured.
Seventy of the assailants were arrested, but they are yet to be charged or prosecuted.
Friday was the sixth day in a row to see clashes in front of Alexandria’s security directorate, with some simply demonstrating against police brutality, and others seeking to penetrate the building.