A man and a woman have been charged following a spate of armed robberies in Melbourne's north-west, including an alleged attempt to steal from a St Albans pokies venue before a heroic punter stepped in.

Police say the series of incidents took place over the last five years at gaming venues, a post office and a liquor store and included four armed robberies and one failed attempt.

Armed Crime Squad detectives arrested a 34-year-old Kings Park man and a 39-year-old Albanvale woman on Wednesday. Police could not confirm whether both were suspected to have been involved in all five incidents.

The man was charged with offences including armed robbery, attempted armed robbery, recklessly cause injury, assault with weapon and firearm-related offences. The woman was charged with armed robbery, theft, trafficking methamphetamine and cultivating cannabis.

Police also seized from two separate addresses imitation firearms, clothing, mobile phones, cannabis plants and a vehicle.