Around 35 Egyptian policemen were wounded when a car blew up near their base in the Suez Canal city of Ismailia on Thursday, security sources said.
Militant attacks on the police and the army have sharply increased in Egypt since the army ousted elected Islamist President Mohamed Morsi in July after mass protests against him.
The security sources said intense gunfire was heard in the area of the police base after the car exploded. It was not clear if the attack was the work of a suicide bomber.
Last month, a suicide car bombing killed at least 10 Egyptian soldiers in the Sinai Peninsula in one of the deadliest attacks there since Morsi's removal.
State authority collapsed in northern Sinai, which borders Israel and the Palestinian Gaza Strip after President Hosni Mubarak was overthrown in 2011, allowing an array of hardline Islamist groups to expand into a security vacuum.
Insecurity worsened after Morsi was ousted, and militant attacks spread to Cairo and other cities following a fierce crackdown by the army-installed government on the Muslim Brotherhood in which hundreds were killed and thousands jailed.
Around 200 police and soldiers have also been killed, according to an army official.