More than 100 people are believed to have been killed at a protest in support of Egypt’s ousted President Mohammed Morsi.

Security forces are reported to have started shooting demonstrators shortly before pre-dawn morning prayers at a round-the-clock vigil in Cairo being staged by backers of Morsi, who was removed from power by the army three weeks ago.

Makeshift field hospitals around the area near the Rabaa al-Adawiya mosque were overwhelmed, with one doctor telling the BBC that more than 1,000 had been injured.