A suicide car bomber killed at least four people at police headquarters in the Egyptian capital, the first of three bombings to rock the Cairo area early Friday.
Security officials say the attacker blew himself up in the parking lot of the downtown facility, in the country's highest profile attack in months.
A few hours later, officials said another blast near a Metro station across the Nile River killed one person and wounded several police officers.
The Interior Ministry says a third attack occurred in Giza, near a police station on the main road to the Pyramids, but there were no injuries.
The blasts occurred early Friday - the first day of the Egyptian weekend - when the streets were largely empty. But the attacks startled residents, who fear an outbreak of violence on Saturday, the third anniversary of the uprising against longtime leader Hosni Mubarak.
No one has claimed responsibility, though Islamist militants have been blamed for a number of attacks against security forces since the country's military ousted President Mohamed Morsi in July.
Television images of the first attack showed extensive damage to the police headquarters, with windows and walls blown out and a large crater in the street. The explosion also damaged the nearby Islamic Museum.
Around 50 people were wounded in the attack, which state television said also included gunmen who opened fire on the police facility.
Egypt's first democratically elected president, Mr. Morsi came to power following the 2011 ouster of the country's longtime military-backed president, Hosni Mubarak.
Mr. Morsi's Muslim Brotherhood, which the government has blamed for past attacks, immediately condemned the bombings, saying it remains committed to peaceful resistance.
Even before the bombings, there were fears of renewed violence. The Brotherhood and the government have called for rival protests on Saturday, the third anniversary of the country's mass protest movement.
The Muslim Brotherhood was designated by the government as a terrorist group following the September bombing of a security directorate in Mansoura, a town north of Cairo, in which 15 were killed.
The al-Qaida-linked Ansar Beit al-Maqdis group claimed responsibility for that bombing, and most of the other biggest attacks, saying they are revenge for the government's crackdown on Islamists.