Officers from the homicide and gangs squad have raided more than a dozen properties across Sydney as part of a major investigation into a string of targeted gangland shootings.

Key points: 13 properties across Sydney raided, at least six arrests made

13 properties across Sydney raided, at least six arrests made Strike Force Osprey set up to investigate eight gangland shootings over past 18 months, including that of Pasquale Barbaro

Strike Force Osprey set up to investigate eight gangland shootings over past 18 months, including that of Pasquale Barbaro Police yet to confirm details of arrests due to ongoing nature of operation

The ABC has been told 13 properties were raided as part of Strike Force Osprey, which was set up last week to investigate eight gangland shootings in Sydney over the past year-and-a-half.

The latest of those was the fatal shooting of mafia figure Pasquale Barbaro, who was shot in Earlwood a fortnight ago.

About half a dozen people are believed to have been arrested in yesterday's raids, including four at Sydney's Olympic Park, but police are refusing to confirm details because the operation is ongoing.

Plain-clothes detectives and riot police were seen yesterday afternoon at an apartment block on Australia Avenue at Olympic Park.

Witnesses said at least one man was arrested in one of the apartments and at least another two people were detained nearby.

Officers later emerged from the multi-storey building with bundles of brown paper evidence bags.

Police have also seized a white sedan and said they planned on seizing a number of other cars from the building's basement car park.

Several officers and a sniffer dog were examining the car.

Police have seized one car and towed two others. ( ABC News: Jessica Kidd )

Police also towed away two other high-powered luxury cars.

Brian Clark, who works in Olympic Park, said he saw police with two individuals who appeared to be under arrest about midday.

"I saw the area cordoned off with police tape, there [were] … police with two individuals bailed up against a wall," he told the ABC.

"Nobody where I work was even aware [something was happening] … there were people going about their business buying lunch unaware anything was going on."