At least 27 people, including several policemen, have been wounded in a car bomb attack in front of a police building in Cairo, according to Egypt's interior ministry.

The powerful blast struck northern Cairo district of Shubra al-Khaima in the early hours of Thursday morning.

"A man suddenly stopped his car in front of the state security building, jumped out of it and fled on a motorbike that followed the car," the interior ministry statement said.

"The car exploded wounding six policemen."

There were no immediate reports of deaths from the explosion, which made a wide crater near the four-storey building, shattered its windows and destroyed a major part of the front portion of a surrounding wall, according to AFP news agency.

A vehicle engine lay metres away from the entrance as police cordoned off the site to prevent crowds of people from gathering, and broken metal parts of a car lay scattered on the ground.

Front glass windows of three buildings near the site were also shattered.

String of attacks

Thursday's blast comes weeks after the Islamic State of Iraq and the Levant (ISIL) claimed a car bomb attack targeting the Italian consulate in Cairo on July 11, which left a passer-by dead.

That attack was the first such targeting a foreign mission in Egypt since the armed groups began their campaign against security forces two years ago after the army's ouster of President Mohamed Morsi in July 2013.

The consulate bombing was followed by the abduction and apparent beheading of Croatian engineer Tomislav Salopek, which the ISIL-affiliated Sinai Province group claimed on August 13.

Armed groups say their attacks are in retaliation for a police crackdown targeting Morsi supporters that has left hundreds dead and thousands jailed.

Hundreds of members of the now banned Muslim Brotherhood have been sentenced to death in mass trials since President Abdel Fattah el-Sisi took control of the nation of 87 million in a coup.

Many of them have won retrials, and Morsi himself, sentenced to death last June, has appealed his verdict.

Though criticised by rights activists, supporters of Egyptian president have backed the crackdown on political opponents.

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The bombing came just days after President Sisi ratified an anti-terrorism law which critics claim gives wider powers to police, restricts human rights and muzzles the press.

The law, published in the government's official gazette on Sunday, sets a minimum fine of 200,000 Egyptian pounds (about $25,000) and a maximum of 500,000 Egyptian pounds for anyone who strays from government statements in publishing or spreading "false" reports on attacks or security operations against armed fighters.

Three journalists had already been sentenced to up to 10 years in prison for "defaming" the country and supporting the blacklisted Muslim Brotherhood movement.

The retrial of three Al Jazeera journalists - Baher Mohamed, Mohamed Fahmy and Peter Greste - was adjourned for a tenth time on August 2.