Fire-generated thunderstorm creates 'very dangerous situation'

A fire-generated thunderstorm has created terrifying apocalyptic scenes and added to the already life-threatening bushfires tearing through NSW.

The NSW Rural Fire Service alerted the Shoalhaven community, south of Sydney, of the aggressive thunderstorm Saturday afternoon, expressing a terse warning to anyone nearby to “take appropriate action”.

A fire-generated thunderstorm has formed over the Currowan and Tianjara fires in the Shoalhaven, and another may form over the Gospers Mountain fire,” the service wrote to Twitter.

“This is a very dangerous situation. Monitor the conditions around you and take appropriate action.”

They also shared a photo from danger zone showing giant plumes of black smoke completely blanketing the sky.

Conditions on Saturday were “as bad as it gets” for areas in in the greater Sydney, Illawarra-Shoalhaven and Southern Ranges regions.

Over 200 additional trucks and firefighters from NSW Fire and Rescue and RFS were allocated to these zones and residents were urged to be prepared to leave.

40 properties lost

Homes have already been damaged in the Lithgow area, on the western edge of the massive Gospers Mountain blaze, as well as in Balmoral where up to 40 properties were earlier lost southwest of Sydney.

There were 112 fires burning across the state Saturday afternoon amid high temperatures and winds, and low humidity.

Temperatures hit the mid-to-high 40s in western Sydney with westerly winds gusting up to 70km/h.

The expected southerly change hit late Saturday afternoon, bringing a large drop in temperatures - in some cases more than 20 degrees. However the risk of changes in fire behaviour and direction remained.

“It's as the change moves through, with that timing, (we're) expecting it to be in the southern part of the greater Sydney area at 5m,” the Bureau of Meteorology's Agata Imielska told reporters earlier.

“That is the most dangerous time and the location will shift with the southerly.”

RFS commissioner Shane Fitzsimmons said the southerly's intensity would deteriorate away from the coast but make life harder for firefighters.

‘Can spread rapidly’

He said Saturday was an awful day for firefighting but milder conditions should ensue after the southerly moved through.

“It turns what was a flank of a fire or a more benign side of the main fire into a fire front that can spread very rapidly in a northerly direction,” Mr Fitzsimmons said.

About 10,000 salaried and volunteer emergency service personnel, including police, SES and ambulance are expected to help to keep residents safe, the largest deployment in the state's history.

Significant road closures are also being predicted and NSW holiday-makers are being urged to be patient, including on the Hume Highway, Great Western Highway, Princes Highway and other arterial NSW roads.

On Friday, 500 residents from two nursing homes, at Kurrajong and Springwood, were evacuated into emergency accommodation.

Saturday's horror conditions come days after the deaths of Horsley Park Rural Fire Brigade volunteers Geoffrey Keaton, 32, and Andrew O'Dwyer, 36, whose truck rolled at the Green Wattle Creek blaze on Thursday night.

Flags were flown at half-mast across the state on Friday for the two young fathers, while members of the 68-strong western Sydney brigade on Saturday put aside their grief to get back to the fire front.

With AAP

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