Bus ablaze on Sydney road

A bus has erupted in flames on a busy Sydney arterial road.

An emergency warning has been issued for a fast moving bushfire in the NSW Hunter Valley. (AAP)

A bus has erupted in flames on a busy Sydney motorway.

Firefighters are working to extinguish the Beecroft blaze, with all passengers safely off the bus.

The M2 is closed to citybound traffic at Beecroft and drivers have been warned to brace for heavy delays.