Egyptian authorities have arrested 18 people they accused of involvement in Thursday's attack on the Nile City Towers in downtown Cairo, which took place at around midday and was followed by other clashes later in the day.

Al-Ahram's Arabic website also reported that the injury toll has reached seven, including three police personnel; a central security forces officer, Ahmed Maher, and two cadets, Ali Farid and Mohamed Nashaat. All three suffered wounds caused by shotgun pellets.

Mohamed Eid, a reception employee at the Fairmont Hotel, was also shot in the left foot while his colleague Ramadan Abdel Latif sustained a similar injury to his right foot.

A satellite television correspondent, Tamer Hamdi, 26, was shot in the left foot, while 18-year-old student, Mohamed Moawad, sustained a shotgun wound to his abdomen.

Al-Ahram also reported that 14 vehicles and six motorcycles were damaged during the turmoil.

A statement issued on Thursday by Orascom Construction Industries, which has an office in the towers, claims that the incident was sparked when a man entered the adjoining Fairmont Hotel and demanded money, threatening people with a knife.

A police officer confronted the man and was attacked, the statement said. The officer shot and killed him.

"Immediately afterwards the residents of the shacks behind Nile City came to attack the hotel and tried to burn it down," it said.

The management of Nile City sealed the building after residents of the area began to burn motorcycles and cars in the forecourt.

Security and emergency services contained the situation, before clashes were renewed late on Thursday after a new attack on the building was carried out.

Investigations into the incident and interrogations with the suspects are still underway.