Five juveniles have been arrested after an allegedly stolen luxury car smashed into a police vehicle at a busy intersection in Melbourne's CBD.

Police had been following the silver Audi from Melbourne's northern suburbs for more than hour before it collided with a police SUV and a civilian truck on the corner of Flinders Street and Kings Way about 1.10pm.

Unmarked police cars and the force's Air Wing helicopter had been on the Audi's tail since it was sighted in Epping at midday but had not initiated a pursuit, according to police.

The car's occupants were also suspects in a series of armed robberies in the North West Metropolitan region, Detective Sergeant Andrew Lawrence, from Darebin CIU, told reporters at the scene.