A low-ranking policeman killed a citizen "by mistake" in the impoverished and populated neighborhood El-Darb Al-Ahamr, Cairo's security directorate said on Thursday.

"A low-ranking policeman was accompanying his relative to buy some goods and when both were uploading goods to a taxi, they had a fight with the taxi driver," the security directorate said in a statement.

"The policeman pulled his gun to end the fight but a bullet came out of the gun by mistake, killing the taxi driver."

The taxi driver is 24-year-old Mohamed Ali Ismail, whose body was transferred to Cairo's Ahmed Maher hospital. The general prosecution is investigating the incident.

According to local news reports, El-Darb El-Ahmar residents staged an impromptu protest at the nearby Cairo security directorate.

"A large number of people gathered in an attempt to catch the policeman but he managed to escape," a security source told Ahram's Arabic news website.

General Khaled Abdel Mataal, the head of the security directorate, met the victim's sister at the directorate to offer his condolences. He promised to arrest the policeman, who is still at large, according to Ahram.