A second explosion has hit Hossary Square in 6 October City, west of Cairo, less than three hours after a first bomb exploded in the busy area and left a police officer with minor injuries, Al-Ahram Arabic news website reported.
No one was injured in the second blast. Security forces closed the street where the bombs detonated and cleared the area in fear of a third attack.
The first explosion involved a homemade bomb planted under a Giza traffic officer's car.
The officer sustained minor injuries and was transferred to a nearby hospital.
Egypt has been hit by a spate of deadly bombings, mainly targeting security forces, since the ouster of Islamist president Mohamed Morsi in July of last year.
The attacks were initially focused on the restive Sinai Peninsula before spreading into strategic Nile Delta cities and the capital.
Last week, three explosions outside Cairo University killed a senior police official and injured five others.
In that incident, two explosions struck with a short time interval between them, followed by a third blast an hour later.