Five people with links to the Comanchero Outlaw Motorcycle Gang have been taken in for questioning.
Police executed warrants about 5.30am at Everitt St Dandenong, Power Rd in Doveton, Lighthorse Crescent in Narre Warren South, Vivien St Dandenong and Princes Way in Longwarry.
Six firearms, cash and drugs believed to be cocaine and steroids were seized.
Two men, aged 25 and 30, and a 21-year-old woman all from Dandenong, a 32-year-old Doveton man and a 32-year-old Narre Warren South man were all arrested at the scene.