Homes feared lost at Mt Tomah and Mt Wilson as Gospers Mountain fire flares up

The Gospers Mountain fire by Monday, had entered the northern part of the Grose Valley around Mt Tomah, and he said crews were working hard to contain the fire.

"Thursday and Saturday are going to be extremely difficult days. Residents need to keep an eye on the Fires Near Me app. If they're not prepared to stay and defend, leave early," Supt Wardle said.

Villages from Wentworth Falls to Winmalee in particular, needed to keep an eye on the Gospers Mountain fire.

"The eastern side of Wentworth Falls to Winmalee need to be vigilant the next few days to a week," Supt Wardle said.

He said on Monday afternoon, that there were some areas in the Megalong Valley that crews were still working on for the Ruined Castle fire, but it was mainly contained, and firefighters had done a lot of work with the Megalong Valley community.

Firefighters were prepared for the hot conditions from Thursday, but he said the fires were unpredictable in these extremely dry conditions.

"With strong north west winds, there is the strong possibility these containment lines will be breached," he said.

"Prepare your property, be vigilant and keep to date with the latest information. If people are not prepared to stay and defend, then leave early."

In Springwood, the Bureau of Meteorology predicts temperatures to reach 42 degrees on Thursday and 43 on Saturday, and in Blackheath it's predicted to get to 38 on Thursday and 40 on Saturday.

UPDATE 12.05pm Monday: A backburning operation that didn't go to plan destroyed structures in the Mt Wilson and Mt Tomah areas, the ABC has reported.

Fire crews lost control of the backburn to the south of the Gospers Mountain fire on Sunday afternoon.

RFS Commissioner Shane Fitzsimmons told the ABC crews in the area were attempting to protect communities around the Bells Line of Road, but "unfortunately things don't always go to plan".

"We've seen how quickly things can change and how destructive the consequences can be," he said.

Assessment teams are expected to determine the exact amount of damage done in those areas today.

8am Monday: Properties around Mt Wilson and Mt Tomah are believed to have been destroyed as the Gospers Mountain blaze was upgraded to emergency alert level on Sunday.

An RFS spokesman said there were reports of properties being "impacted" but they were not yet able to confirm specifics. The fire was downgraded to watch and act level overnight.

Blue Mountains mayor Mark Greenhill said the unconfirmed reports of property impacts in the mounts "is the news we did not want to hear".

"Emergency services have been working hard for weeks preparing and those are very prepared communities. However, if property has been impacted we need to be there to support those who have to walk the journey of recovery.

"It is my fear, given the fires around our community, that we have very difficult weeks ahead."

The Terrey Hills RFS Brigade posted a video on Sunday of 70m high flames in Mt Tomah.

The RFS advised people in Mt Tomah, Mt Wilson, Mt Irvine and Bilpin on Monday morning that the fire activity had reduced and there was no immediate threat. Embers may still fall ahead of the main fire front.

The Bells Line of Road is closed at the Mount Tootie Road intersection.

The Blue Mountains Botanic Garden at Mt Tomah posted on its website on Monday: "We are still assessing the extent of the damage, however the impact on some parts of the Garden appears to be significant. Thankfully, most of the Garden's Living Collection along with the main buildings are safe at the moment."

Cr Greenhill said "our exhausted emergency services had a hard day yesterday and many hard days ahead".

"The situation unfolding will be tough and the conditions unprecedented. Now more than ever, we need to find that wonderful community spirit we are known for."

For fire updates visit Fires Near Me.