A 10-year-old boy has been found living at a Blue Mountains property where a raid uncovered 310 cannabis plants and other illegal drugs, police say.

Eleven people were arrested in the early morning raids on five homes in Katoomba and Leura on Wednesday.

It follows a six-month investigation by Strike Force Elrond into the supply of illegal drugs in the area.

Police said on Thursday they found and seized 310 cannabis plants and four kilograms of cannabis with an estimated street value of more than $470,000.

Heroin, cocaine and amphetamines were also seized from the same property.

“The concerning part about that premises is that we found a 10-year-old who was staying there,” Assistant Commissioner Denis Clifford told reporters.

Police said they were working with the Department of Community Service to find suitable living arrangements for the child.

Asst Comm Clifford said the raids were the result of a tip-off from a member of the community about suspicious activity.

“We encourage anyone who has any suspicions about activity in their area to pass it on to us.”

Nine men aged between 24 and 54 and two women aged 25 and 51 have been charged with more than 70 offences.

They include cultivating a commercial quantity of a prohibited plant; supplying a large commercial quantity of amphetamine; supplying amphetamine, cocaine, ecstasy and cannabis on an ongoing basis; possessing a prohibited drug; and dealing with property suspected to be the proceeds of crime.