Fire crews from Chorley and Preston were called out to a grass fire near Rivington Pike.
Residents spotted the flames on the hillside, close to the Chinese Gardens, at around 7.45pm on Sunday.
Images posted on social media showed smoke pouring from the hillside and the fire visible from afar.
One witness reported being able to see the flames from the M61 motorway.
When the Lancashire crews arrived, the flames were already under control by members of Greater Manchester Fire and Rescue Service.
It is unclear how the fire started. It not thought that anyone was hurt.