Six people have been charged with heroin trafficking in an operation targeting a suburb in Melbourne's west.

Police arrested 40 people as part of the five-week investigation into the drug trade in Footscray's commercial centre.

More than 100 charges were laid, including 60 for trafficking heroin and 20 charges for possessing drugs including heroin, amphetamines, cannabis and prescription drugs.

A number of weapons were also seized including knives and a small pen pistol.

Detective Senior Constable Brendan O'Mahoney said more people were expected to be interviewed in coming weeks.