An estimated $275,000 worth of drugs hidden in the "internal cavity" of a car have led police to the discovery of 250 cannabis plants and weapons in Melbourne's east.

Police arrested seven people after raids in Croydon, Croydon Hills, Kilsyth and Mount Evelyn on Wednesday night, seizing an estimated $640,000-worth of drugs, a gun, a knuckleduster and a large amount of cash.

"As a result, a complex and well-organised drug trafficking syndicate has been dismantled, a significant quantity of illicit drugs has been kept off the streets and several principal offenders have been charged,” Detective Senior Sergeant Jim Sutherland said.

The breakthrough came when police intercepted a Kia Sportage at a service station on the Melba Highway, in Glenburn, just after 9pm.

After finding the alleged drug stash, police arrested the two occupants – a Croydon man, 26, and a 22-year-old Croydon Hills man – who will front Melbourne Magistrates Court on Thursday.

The subsequent raids ended in charges to a Mount Evelyn man, 26, who will also appear at Melbourne Magistrates Court on Thursday.

A Croydon woman, 24, and a Kilsyth man, 55, are due to appear at Ringwood Magistrates court in February next year.

Two men from Croydon, aged 24 and 26, were interviewed by police and are expected to be charged on summons.