The moment a passenger train went through a Sydney bushfire

Trains on Sydney's Airport Line were disrupted by the bushfire. Photo / Twitter, @T8SydneyTrains

'It's jumped the line already': Train drives through Sydney bushfire https://t.co/uyBRijVeWe Pic: Twitter / Facebook pic.twitter.com/4CBBcL0nEP

— ABC Sydney (@abcsydney) April 14, 2018

A bushfire that's burned almost 1000ha in Sydney's southwest remains out of control but has been downgraded as conditions ease and crews begin back- burning operations.

The fire resulted in hundreds of people being evacuated from their homes last night with flames almost reaching properties at Holsworthy and Wattle Grove and spot fires later threatening Sutherland and Menai.

ABC Sydney reports that at one point a passenger train went through the fire and the journey was caught on camera.

Flames and spot fires can be seen near the carriages in the video which was posted to social media.

ABC Sydney says part of the line was later closed.

Today the NSW Rural Fire Service downgraded the bushfire to a "watch an act" alert.

"Residents in the area of Sandy Point and Alfords Point should continue to monitor the conditions as they could change quickly," the RFS said in an alert.

"Residents in Illawong, Bangor and Picnic Point are experiencing ember attack and should continue to monitor for any new spot fires in the affected areas.

"Firefighters are in these areas and are ready to undertake property protection if required."

Heathcote Road remains closed between Macarthur Drive and New Illawarra Road. The RFS said the easing conditions had allowed firefighters to begin back burning along Heathcote Drive.

The threat to properties has reduced but "winds will strengthen across the day", the service warned.

Police believe the fire may have been deliberately lit and are appealing for witnesses to contact them. Sydney is expecting a top of 25C today with westerly winds up to 40km/h.

- AAP