Westlink M7 crews are installing signs, cutting the grass and getting the drinks stations ready for some 200 runners competing in the event offering a $50,000 prize pool.

Starting in Liverpool, the marathon route will take runners along the M7 shared path for 30 kilometres before turning back towards the finish line at the Blacktown Olympic Park in Rooty Hill.

Westlink will have six staff working with Blacktown Council and other authorities on the day to make the marathon a success.

The shared path will be closed to the public during the marathon from 6am to 1pm.

Westlink general manager Rachel Johnson said all staff had been working hard to ensure the pathway would be ready for the marathon.

``Over the past three months we've planted over 8000 native trees and colourful shrubs along the shared path from Camden Valley Way to Old Windsor Road,'' she said.

Ms Johnson said the event was gaining increasing national and international interest.

``The runners love it as the route is traffic-free and uninterrupted, making it safe and enjoyable to run.''

The Westlink Cities Marathon, which is accredited by the International Association of Athletics Federation, attracted over 150 competitors last year.