About 200 firefighters and five helicopters have battled to contain a major blaze in the Blue Mountains, with temperatures topping 45 degrees in parts of NSW.

An emergency fire warning remains in place for the Blaxland-Warrimoo area after being issued on Friday afternoon.

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The fire service upgraded the out-of-control blaze between Blaxland and Warrimoo to the highest level of bushfire alert about 3.30pm.

Residents were advised to evacuate homes while there were fears for school children in the area.

But students at Warrimoo Public School and Blaxland School were later confirmed safe.

The fire crept dangerously close to properties in the area, while the Great Western Highway was temporarily closed and the train service put on pause between Glenbrook and Springwood on the Blue Mountains Line.

“It’s been a tough day for firefighters but the fire condition has certainly eased a little, but we’re still holding the warning in place because we’ve got quite a few hours to go yet,” NSW RFS Commissioner Shane Fitzsimmons told ABC News.

He added that if the fire wasn’t already challenging enough, aircraft were also hampered by the fact the blaze was burning under “some very significant high-voltage power lines”.

By Friday evening the fire was still burning southeast towards Baden Place, Blaxland, the fire service said.

Temperatures are expected to be cooler in the Blue Mountains on Saturday with a top of 27 and a chance of afternoon showers.

There are total fire bans in place on Saturday for the Hunter, Central Ranges, Northern Slopes, North Western, Upper and Lower Central West Plains.