Five makeshift bombs exploded at four Cairo metro stations on Wednesday morning, wounding at least five people, while another detonated near a courthouse in the capital, officials said.

Militants have stepped up attacks in Egypt, mostly against security forces, since the army ousted Islamist president Mohamed Morsi in July 2013 and the authorities launched a deadly crackdown on his supporters.

Four bombs exploded within minutes of each other at three metro stations as commuters made their way to work during morning rush hour, while a fifth went off hours later at another station, a police official told AFP.

One struck at Ghamra station, in central Cairo, and the others hit Hadayek al-Kobba in the north, and Shubra al-Kheima and Ezbet al-Nakhl on the outskirts of the capital.

All of the blasts were caused by "very primary" devices of "low intensity" that were placed in trash cans on platforms of the stations, the police official said.

Four people were wounded by the first string of blasts, senior health ministry official Ahmed Al-Ansari told AFP, while a fifth was hurt in Ezbet al-Nakhl, the police official said.

Interior ministry spokesman Hani Abdel Latif said a man who had been carrying one explosive device in his bag was among the wounded at Shubra al-Kheima.

Latif said the man "appeared to be a Muslim Brotherhood member" as an image of a four-finger salute used by Morsi supporters was found on his telephone.

The authorities have blamed the Brotherhood, from which Morsi hails, for the attacks rocking the country and have blacklisted the Islamist movement as a terrorist organisation.

Another makeshift bomb placed under a car exploded near a courthouse north of Cairo, wounding a woman, and a second was defused at the site, said Abdel Latif.

The attacks come after a court last week confirmed death sentences on 183 Islamists, including Brotherhood chief Mohamed Badie, and nearly a month after Abdel Fattah al-Sisi, the ex-army chief who led Morsi's ouster, was elected president.

Since Morsi's ouster, a crackdown on his supporters has left more than 1,400 people dead and seen at least 15,000 jailed.

Much of the violence is focused in the north of the Sinai Peninsula, but militants have extended their reach to Cairo and the Nile Delta, carrying out a series of high-profile assaults in the heart of the capital.

An Al-Qaeda inspired jihadist group based in the Sinai, Ansar Beit al-Maqdis (Partisans of Jerusalem), has claimed some of the deadliest attacks on security forces, as well as a failed assassination attempt against the interior minister in September.

A little-known jihadist group, Ajnad Misr (Soldiers of Egypt), has also claimed a string of attacks on police in Cairo.

The government says the militants have killed about 500 people, most of them security personnel.