Twelve people have been arrested and drugs, cash and weapons seized by Victoria Police's anti-bikie taskforce this week.

Echo Taskforce detectives raided eight properties on Tuesday and four on Thursday in south-east Melbourne as part of an investigation into an alleged drug trafficking syndicate.

Seven men and two women were arrested on Tuesday on drug, weapons and proceeds of crime offences after police raided properties in Keysborough, Cranbourne North, Springvale South, Mulgrave and Dandenong North.

Drugs including heroin, methamphetamines and cannabis, as well as what police believe to be chemicals used to make drugs, were seized, as well as a motorcycle, jewellery, and weapons including pistols and tasers.

On Thursday, police raided four properties in Narre Warren South, Dandenong North and Springvale South, arresting three men and seizing cash.

Six of those arrested on Tuesday have faced Dandenong Magistrates' Court, with three in police custody and three bailed to appear again.

A further three men will appear at a later date.

Three other men, arrested on Thursday, were charged with drug offences and faced Dandenong Magistrates' Court with one in police custody and two on bail to appear at a later date.