A building in Egypt's capital, where two floors had been added illegally, collapsed overnight, killing 15 people and burying seven more in the rubble, emergency services and officials said Tuesday.

At least seventeen people were killed and three were still under the rubble when a residential building in Egypt’s capital collapsed overnight, emergency services said on Tuesday.

Countless buildings in the teeming city of more than 20 million have been put up in defiance of the most elementary rules of construction, often without permission, rescue services say.

The owners had illegally added two additional floors to the seven-storey building in the poor Matariya district in the east of the city.

“Seventeen people have been killed, eight injured and three are still under the rubble according to their relatives,” Cairo’s emergency services head General Mamduh Abdelkader told AFP.

He said investigators were still investigating the cause of the collapse but that illegal construction work was suspected.

“We don’t yet know the cause of the accident but we have been told that two storeys were recently added totally illegally,” Abdelkader said.

An AFP journalist said rescuers working to clear the debris were struggling to manoeuvre their equipment in a very narrow alleyway.

Relatives of the missing and onlookers were digging with their bare hands in the rubble.

A woman who said her brother died in the collapse charged that the building was so unsafe she had refused to enter it.

“When I would come to see my brother I refused to come inside because the building was too fragile. I told my brother and all inhabitants they had to leave,” she said.

Residents both of the building and the neighbourhood told AFP of construction work and two floors added illegally.

Mohammed al-Bishlawy, district prosecutor for eastern Cairo, told AFP he has opened an inquiry and asked for the arrest of the building’s owner.

He blamed the accident on “renovation work in a second-floor apartment that has affected the structure of the building and the addition of two floors without permission”.

There have been several deadly building collapses in the past few years in Egypt, where safety and planning regulations are widely flouted.

Landlords often add extra floors to buildings whose foundations were not designed to support them.

In January 2013, 17 people were killed when an eight-storey building crumpled in Alexandria, a few months after the collapse of an 11-storey block in the Mediterranean city killed 19.