Passenger films raging bushfire just metres from train window

A train passenger has filmed a raging bushfire, southwest of Sydney, through a carriage window.

Trains have been significantly delayed in the Holsworthy area with a partial closure between East Hills and Glenfield due to the bushfire. Buses are replacing trains.

The footage, shot at Holsworthy, shows plumes of smoke rising into the sky as the train nears the area of disaster.

The video then cuts to the train travelling past a bush area where trees and grass can be seen going up in flames.

There appears to be spot fires in a number of areas with passengers forced to look on in horror.

One person commented on the video and said "seems like a hazard".

"If a tree fell down, you're stuck in the middle of a fire ," the person wrote.

"I'm looking out my window in ... the distance there is just orange smoke. Everything is on fire ," another person said.

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The bushfire raged overnight forcing residents from their homes. Some decided to stay back to try and protect their livelihood from going up in smoke.

The NSW Rural Fire Service issued a fresh alert about 12pm Sunday saying it was too late for residents of Alfords Point, Menai and West Barden Ridge to leave the area after the fire was upgraded to emergency status.

It said there had been increased fire activity with strong winds and embers sparking new fires.

“Voyager Point, Pleasure Point and Sandy Point are experiencing ember attack. Residents in these areas should shelter in place. It is too late to leave,” the warning said.

Earlier, NSW Premier Gladys Berejiklian said it was "miracle" no lives or properties were lost when a bushfire raged through southwest Sydney overnight.

The blaze had initially started as a grass fire but soon became an out-of-control bushfire.

NSW police say they believe it could have been deliberately lit but they are continuing to investigate.