Homes threatened as bushfire burns near southwest Sydney

The fire, which began on Saturday afternoon and may have been deliberately lit, was fanned by strong winds on Sunday and approached suburban streets.

The bushfire was downgraded to "watch and act" yesterday evening, replacing the emergency warning put in place, and this morning was further downgraded to "advice" level.

Some remembered bad bushfires in the 1990s when homes were destroyed, and were determined to stay and extinguish embers or spot fires as they broke out.

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

A blaze at Menai still continues to burn in a south easterly direction toward Barden Ridge - no homes are at risk but crews are on the ground focused on containing the fire. (AAP) Thick smoke has blanketed most of Sydney over the weekend.

"This huge blaze has been fought in very high temperatures, very high winds, unseasonal conditions, and has been done so in a way which has seen, to date, no injuries and no serious damage to property", Mr Turnbull said.

Residents in the suburbs of Voyager Point, Pleasure Point, Sandy Point and Illawong, Menai and Bangor were warned of the danger of ember attacks as many scrambled with hoses and buckets to protect their houses.

Many residents in Menai chose to remain at their homes and were kept busy fighting ember attacks.

Daniel Borg, who lives on Hall Drive in Menai alongside bushland, admitted it was concerning to see how close the flames came.

Police believe the fire may have been lit on goal and are appealing for witnesses to contact them.

Conditions on Monday are expected to help the firefighting effort but winds could pick up to 35km/h later in the day.

The Transport Management Centre said Heathcote Road remained closed between New Illawarra Road and Macarthur Drive, and there was no forecast for when the road would be reopened.

"I think we've got a long way to go before we're out of the woods", he said.

"Residents around that area should monitor the situation, take advice from firefighters in the area and know what they'll do if fire threatens", he said.