Bushfires are blazing out of control on opposite sides of the continent with homes threatened outside both Sydney and Perth.

Homes are thought to have been lost in the path of a major blaze in the Wollemi National Park, northwest of Sydney, where residents were told it was too late to leave.

On Sunday, 106 bush and grass fires were continuing to burn across NSW, with 57 not yet contained. On Monday, total fire bans will be in place for five areas of NSW - Far North Coast, Central Ranges, New England, Northern Slopes & North Western.

In Western Australia, a new bushfire is threatening lives and homes in Mogumber, north of Perth. An emergency warning has been issued and residents have been asked to shelter.

NEW SOUTH WALES

Close to Sydney, residents faced an emergency warning for the Gospers Mountain blaze on Sunday. This huge fire was almost 370,000 hectares in size.

The ABC reported flames up to 70 metres high had been seen and several homes in the Hawkesbury were lost. Others said the flames were up to 20 metres high.

The so-called mega-fire flared, growing "considerably" at the southern end Sunday afternoon.

The NSW Rural Fire Service (RFS) said the fire has crossed Bowen Creek, south of Mount Wilson. The blaze moved towards Mount Wilson, Mount Irvine, Mount Tomah and Berambing and winds were creating spot fires ahead of the main fire front.

Mount Tomah is the home of the heritage listed Blue Mountains Botanic Gardens one of the region's major landmarks known from its cool climate plants that would fare less well at lower elevations closer to Sydney.

The Bells Line of Road, one of two roads across the Blue Mountains, was closed between Bilpin and Bell. It passes the Blue Mountain Botanic Gardens. Motorists were told to avoid the area and use the Great Western Highway instead.

Smoke from Gospers mountain fire. Photo / Instagram

For residents in these areas the RFS advised that fire activity was increasing: "It is too late to leave. Seek shelter as the fire approaches. Protect yourself from the heat of the fire."

"This large fire stretches from the Lithgow area in the west, through the Hawkesbury area and towards the Central Coast in the east," the RFS stated.

Places such as Cobar, Broken Hill and Griffith will see temperatures above 40C in the coming week, the Bureau of Meteorology said. Some 724 homes, 49 facilities and 1582 outbuildings had been destroyed so far this fire season. Six people have died and 2.7 million hectares have been scorched.

WESTERN AUSTRALIA

In WA, firefighters are battling a blaze north of Perth, near Mogumber, that's already burned through almost 12,000 hectares.

An emergency warning was issued and residents asked to shelter. The bushfire is out of control and moving fast in a north-easterly direction. Thousands of properties have been saved from another bushfire raging out of control at Yanchep, around 100 kilometres west from Mogumber, but authorities said the threat isn't over.

The Yanchep blaze remains at an emergency warning after firefighters protected more than 6000 homes from the near-12,000 hectare blaze.

One house and a Yanchep service station are confirmed to have been lost. "If you look at where the fires have gone, it is absolutely astonishing that we haven't lost more than one house," Emergency Services Minister Fran Logan told reporters on Sunday.

But communities are warned to remain vigilant, with Perth and the fire area forecast to reach 40C for the third day running. Lives and properties are under threat at Guilderton, Woodridge, Gabbadah, Wilbinga, Caraban, Seabird, Yeal, Redfield Park, Sovereign Hill, Seatrees and Breakwater Estates.

A Boeing 737 fire fighting aircraft sent from NSW to help in Western Australia. Photo / NewsComAu

HELP ARRIVES FROM EAST COAST FIRES

Earlier on Sunday morning, Australia's biggest firefighting aircraft landed in Perth to assist firefighters battling the massive blazes, as bushfires continue to burn across the country.

The Boeing 737 tanker flew to Perth from NSW overnight to assist as forests near the north Perth suburb of Yanchep burn.