Egyptian police say they have arrested a suspect in a drive-by shooting that seriously wounded a protester in Cairo's central Tahrir Square, where an open-ended sit-in is taking place.

According to witnesses, gunmen before dawn on Monday seriously wounded 19-year-old Mohannad Samir, who has said he was jailed and tortured under Egypt's former ruling military council after he witnessed the killing of another activist Ramy El-Sharkawy in the clashes of cabinet HQ last December 2011.

Lawyers say the attacked appeared to target Samir, who is battling for his life with pellets embedded in his head. Samir is a member of the influential 6 April Youth Movement, which played a pivotal role in ousting autocratic leader Hosni Mubarak in an 18-day uprising in 2011.

Officials said Tuesday they arrested a cafe owner who told police that he fired on the square after people manning makeshift checkpoints there searched his car and shot at him. Police suspect two others were with him.

Police spoke anonymously in line with regulations.