Authorities have arrested three supporters of Mohamed Morsi outside the Cairo police academy where the trial of the ousted Islamist president begun on Monday, according to an Ahram Online reporter at the scene.

Security forces fired in the air to disperse anti-Morsi crowds after they clashed with Morsi loyalists converging outside the police academy, located on the outskirts of Cairo.

At least 18 others were arrested in the Mediterranean city of Alexandria on Monday after clashes erupted between pro- and anti-Morsi protesters.

Morsi's supporters have been protesting since early morning in Cairo and other cities against the trial of the deposed leader on charges of inciting the murders of protesters in December 2012.

The president's backers have slammed the trial as illegitimate and undemocratic.

Morsi, who had been held at a secret location by the military since his ouster in July after mass protests against his rule, made his first public appearance since the ouster in court on Monday morning.

The charges relate to the deaths of ten people and the injury of 600 in violent clashes between Morsi’s opponents and supporters outside the presidential palace in December 2012, after thousands took to the streets to protest a Morsi decree expanding his powers.

Footage which circulated on social media outlet showed Brotherhood supporters at the presidential palace abducting, beating and abusing anti-Morsi demonstrators for hours at a time during the clashes.

On Monday, the trial was adjourned to 8 January, and judicial sources said the president would be transferred to Alexandria's Borg Al-Arab prison.