Two men are facing terrorism charges following raids in Melbourne yesterday.

An investigation into a fire lit at bushland near Epping a month ago, and a public assault in the CBD on March 10, turned into a counter-terrorism investigation that culminated in raids in Epping and Pascoe Vale.

Two Epping men, aged 19 and 20, were questioned overnight.

The 19-year-old has been charged with attempted terrorist attack, intentionally cause injury, act in preparation of a terrorist act, and membership of a prescribed terrorist organisation (ISIS).

Meanwhile, the 20-year-old man suffered a medical episode in police custody. He has been taken to hospital under police guard.

He will also face the Melbourne Magistrates Court today charged with one count of attempted terrorist attack.

A 16-year-old Pascoe Vale boy who was arrested in the raids yesterday has been released without charge.

Police say there is no ongoing threat to the community.