As the day unfolded: ADF reserves called up, fires at emergency level, more helicopters and ships dispatched

About 155 bushfires continued to burn across NSW on Saturday night, including a number of rapidly-expanding blazes, as a southerly change brought strong winds and lower temperatures.

Seven bushfires were at "emergency" level at midnight, down from a peak of 13 fires burning at the highest warning level on Saturday evening.

Another 11 fires were at "watch and act" status and 136 were at advice levels.

About 32,700 homes would remain without power overnight in Batemans Bay and Moruya and fires threatened major sources of power supply in the Snowy Mountains and other parts of the state.

NSW experienced severe fire danger on Saturday with temperature records tumbling in Sydney and Canberra.

However, a southerly change came through the state, bringing gusts of up to 128 kilometres per hour in the state's south-west on Saturday evening.

It also brought a spate of fast-spreading fires to the state's south, including a new fire near the Shoalhaven region and an expanding blaze that threatened residents in Eden and surrounds.

Prime Minister Scott Morrison issued a compulsory call-up to 3000 Australian Defence Force reservists to help communities affected by fires in NSW, Victoria, South Australia and Tasmania.

Cooler temperatures are expected to somewhat ease the fire danger on Sunday but a total fire ban will remain in place across the state.

Read our day's wrap here.

A large water reservoir has collapsed in Cooma in NSW's south, injuring one woman and flooding streets and homes.

The North Ridge reservoir, which is believed to have had a 4.5 million litre capacity, burst on Saturday night.

"Streets and homes in Cooma have been flooded after a water tank burst, sending thousands of litres of water through the town," NSW police said.

"A car was swept 800 metres down the road into a truck, with other cars also subsequently damaged.

"One woman has sustained minor injuries and has been taken by paramedics for treatment."

Residents called emergency services shortly after 9.15pm on Saturday when the reservoir, which is one of two tanks that supplies the town with water, burst.

The second tank remains intact and drinking water is still available to the town's residents.

Local council officers are helping police check reports of water damage to homes and buildings.

It is not yet known whether the incident was related to fire activity.

There is an out-of-control vehicle or equipment fire burning along the Monaro Highway in Cooma and several fires at "emergency" level surround the area, including the Adaminaby Complex, Good Good and Doubtful Gap Trail fires.

The RFS also issued warnings about fire-generated thunderstorms in the area on Saturday afternoon.

A fire that is "spreading quite quickly" is threatening areas north of the Shoalhaven River, including Bundanoon, Avoca, Exeter, Fitzroy Falls, Wingello, Penrose, Meryla and surrounding areas.

Another blaze, the Border Fire in the Bega Valley, is now threatening Eden, Burragate, Towamba, Narrabarba, Kiah and Womboyn as strong winds push fires to the north.

Residents in the path of both fires, which are burning at "emergency" level, are being told that it is too late to leave and they should seek shelter.

"The [Morton] fire is spreading quite quickly, anyone in its path as it moves north is under threat," an RFS spokesman said on Saturday night.

He said it is suspected the Currowan fire that is burning at "emergency" level in the Shoalhaven spotted north across the Shoalhaven river to become the Morton blaze.

"Firefighters are responding and a number were already in the area, this is a fire that will be evolving throughout the night and is of concern to us," the spokesman said.

Winds of up to 104 kilometres per hour have been recorded in Kurnell in Sydney's south and the city's north may experience even stronger gusts as the southerly change moves through.

The change was about "halfway through Sydney" at 9.50pm on Saturday and will hit the northern suburbs in the next 30 to 45 minutes, Bureau of Meteorology's duty forecaster Jake Phillips said.

The winds have also brought temperatures down from the mid-30s to the mid to high-20s.

"That will drop a bit more as the southerly becomes settled," Mr Phillips said.

The change will continue moving through to the Hunter on Saturday night and Sunday morning and will bring cooler temperatures and a slightly lower fire danger on Sunday.

There are also concerns the change will exacerbate bushfires that continue to burn across NSW.

There are currently 10 fires at "emergency" level and 11 at "watch and act".

Penrith reached the highest temperature ever recorded for the Sydney basin on Saturday, with the mercury peaking at 48.9 degrees at 3.02pm.

The previous record for Sydney was 47.8 degrees, set in Richmond in 1939.

"It's the hottest known temperature for the Sydney basin for any month," duty forecaster at the Bureau of Meteorology Jake Phillips said.

Canberra also achieved a temperature record on Saturday, with a maximum of 44 degrees at the airport.

The previous record for that site was from 1968.

Mr Phillips said the new records would stand for at least the rest of the week, with a cool change to bring temperatures down to 25 degrees in Sydney and 29 degrees in the city's west on Sunday.

Footage taken from the Himawari-8 weather satellite run by the Japan Meteorological Agency is showing plumes of smoke coming off Australia's east coast, as hundreds of fires burn across NSW and Victoria.

The two people killed in a bushfire on Kangaroo Island have been identified as well-known local pilot and his son.

Dick Lang ran a tourism business out of Adelaide Airport and his son Clayton Lang was a respected plastic surgeon.

The Lang family said the pair were in the process of returning to the family property on Kangaroo Island after fighting a nearby fire for two days.

"We are devastated to have lost two beloved members of our family - Dick Lang and his youngest son Clayton Lang - in such terrible circumstances.

"He [Dick] loved the bush, he loved adventure and he loved Kangaroo Island.

"Clayton, 43, was one of Adelaide's leading plastic and reconstructive surgeons, specialising in hand surgery. He was supervisor of surgical training and clinical lead of hand surgery at The Queen Elizabeth Hospital. He also consulted privately."

Read the full story here.

The NSW energy minister Matt Kean has urged residents across the state to reduce electricity usage as the Berejiklian government scrambles to determine the extent of fire damage to the Snowy Hydro's transmission lines.

The NSW grid's links to Victoria went down late on Saturday afternoon, with Mr Kean issuing a statement urging all residents to preserve power.

The Australian Energy Market Operator (AEMO), TransGrid and the NSW and ACT Governments were working closely "to keep power supplies on" but weather conditions meant authorities could struggle "to keep the overall system secure.”

Read the full story here.

The southerly change has hit the Shoalhaven, pushing a major blaze at the top of the Currowan fire northwest towards Bundanoon or the Kangaroo Valley.

Dense smoke west of Nowra as the southerly moves through on Saturday evening.Credit: Nick Moir

Visibility has been reduced to just metres as thick smoke from fires to the south billows over Nowra.

Firefighters near Tapitallee were pulled back from dangerous sections of the Currowan fire, which is burning at an "emergency" level.

Much of Tipatallee has been evacuated, though some residents and animals remain.

About 32,700 people in Batemans Bay and Moruya lost power for the second time on Saturday at about 7pm and outages will remain overnight.

"Power will not be restored overnight as safe access is not available into the damaged area," a spokeswoman for Essential Energy said.

"An estimated time for when power will be restored to these customers will be available once we can gain safe access to the network."

"Emergency" level fires continue to burn at the Kings Highway in Eurobodalla and at Clyde Ridge Road in the Shoalhaven.

About 30,600 residents in those areas first lost power on Saturday afternoon.