More than 130 firefighters were working to contain the 30-hectare blaze at Wentworth Falls on Saturday afternoon, with many crews waiting in and around homes near the fire in case a wind gust blew embers towards the properties.

Fire activity calmed in the area early on Saturday afternoon, with two waterbombing helicopters dealing with any flare-ups, but the blaze was still listed as out of control.

Fire crews were able to get the upper hand when winds forecast for 3pm were not as strong as expected, but the winds could make a return on Sunday, RFS Inspector Ben Shepherd said.

"So by no means are we out of the woods yet, but it looks like, given it was supposed to peak by 3pm and we still haven't seen those winds, it's enabled us to really get the upper hand on the fire," Inspector Shepherd said.

"At this stage, they are saying that we possibly could see a return to the strong winds tomorrow, but we can do some good work overnight in trying to get some of these containment lines in."

Once the fire is brought under control, investigators will move in to find out how the fire began.

"The fire I believe is now being treated as suspicious," Inspector Shepherd said.\

"The fire investigators will be called. They're just waiting for fire activity in the general vicinity to subside, but they'll move in there and just try to determine the cause and the origin."

The fire was burning in a northerly direction in an inaccessible area down a cliff near Hordern Road, Coronation Road and Tableland Road. Crews were concerned it would threaten homes on a nearby escarpment.

"There are still homes that are close to this fire, and it doesn't take much - all it takes is a little bit of flare in the wind and we can see it escalate and escalate quickly," Inspector Shepherd said.

The fire broke out on Friday night at around 8pm and gained momentum on early Saturday morning.

Residents were woken by emergency alert calls and text messages at 4am when the fire climbed to heights of up to six metres and firefighters were concerned homes could be impacted.

"The residents were initially aware of the fire around about midnight," Inspector Shepherd said.

"A lot of those residents actually went to bed. Then we saw another escalation of that fire around 4am, which resulted in us sending that alert, because it was running hard at that stage. No further alerts have been sent [but] there hasn't been an all clear sent either."

Residents have been reminded to keep an eye out for burning embers which may start spot fires ahead of the main fire front.