Three policemen were killed in Mansoura, Daqahliya governorate in the early hours of Monday when unknown assailants attacked a security checkpoint.
Eyewitnesses said around four assailants on motorcycles opened fire at the checkpoint on the outskirts of the Nile Delta city, Al-Ahram Arabic news website reported.
Initial investigations by the general prosecution found 60 bullet casings at the scene.
Heavy security has been deployed in the area.
Egypt has been gripped by unrest since the army overthrew Islamist president Mohamed Morsi on 3 July amid mass protests against his rule.
Armed attacks on security units have been occurring regularly across the country since then, particularly in strategic areas with a heavy police and military presence, such as the Suez Canal cities and North Sinai.
More than 100 soldiers have been killed in the Sinai Peninsula since early July, the army said last month.