Amateur footage captured the second blast as it went off near Cairo University
A police brigadier-general has been killed as three bombs went off near Cairo university, Egyptian state media say.
At least five other people were injured in the attacks, authorities say.
The first two bombs went off within minutes of each other, with the third coming about two hours later.
Egypt has witnessed several attacks against government targets by militant groups, following the ousting of the Muslim Brotherhood in July.
The latest explosions happened near a police post outside the university’s faculty of engineering.
State TV named the officer as Tariq al-Mirjawi, the head of Giza’s investigation department.
“I was waiting for the bus when I heard two explosions. There was dust in the air and policemen were screaming” an eyewitness told AFP.
The third explosion took place as journalists and emergency workers attended the scene, but was reportedly much smaller than the first two and caused no casualties.
The BBC’s Orla Guerin in Cairo says the area around the university has become a battleground for clashes between police and Muslim Brotherhood supporters in recent weeks.
The current government has outlawed the Muslim Brotherhood, declaring it a terrorist organisation.
It accuses the movement of supporting attacks against the police and army – a claim the Brotherhood strongly denies.
Since the overthrow of the Brotherhood’s Mohammed Morsi, more than 1,000 people have been killed and thousands of members have been detained in a crackdown by the interim authorities.
The government says militants have killed almost 500 people in the same time period, most of them policemen and soldiers.