A man has been arrested following an alleged armed robbery in Frankston yesterday evening.

Investigators have been told a man entered the Nepean Highway service station about 5.50pm and went in to a public toilet.

A short time later the man exited the toilet, approached the counter and allegedly threatened an employee with n edged weapon.

He stole an amount of cash before fleeing the scene in a Holden Commodore.

An off-duty police officer sighted the Holden driving erratically in the vicinity of Oliver’s Hill where it crashed into a Nissan Navara.

The 24-year-old was arrested a short time later as he attempted to flee on foot towards the foreshore.

He is currently in custody assisting police with their enquiries.