A four hectare grass fire at Plumpton has shut the south-bound lane of the M7 motorway.
Cumberland Rural Fire Centre said the blaze started around 11am but the cause is not known.
Seven fire crews from the Rural Fire Service and Fire and Rescue NSW are on the scene.
Inspector John Bennett, from the Cumberland Rural Fire Centre, said crews needed to close the south-bound lanes due to large amounts of smoke and poor visibility in the area.
‘‘There’s low fire danger today and we’re lucky the conditions are in our favour with no wind,’’ Inspector Bennett said.
The motorway is expected to be re-opened this afternoon.