Six teenagers have been charged over five robberies carried out in the space of an hour on a Melbourne street in the city's south-east.

The boys, aged between 15 and 17, were arrested while driving in a Holden Commodore on the Eastern Freeway in Kew, in Melbourne's inner east, about 9pm on Thursday.

Police believe the car, which allegedly had stolen number plates, ran out of petrol on the freeway.

An unloaded firearm was discovered near the car.

The group was arrested about 30 kilometres from Wright Street in Clayton where police allege they carried out five robberies in an hour.