Massive Sydney bush fire closing in on Lucas Heights nuclear reactor

A massive bush fire burning in Sydney's southwest is getting closer to Australia's only nuclear reactor.

The bushfire on Sydney's outskirts, which has been burning since Saturday, has so far burnt through more than 2400 hectares.

The AM Show Australian correspondent Jason Morrison described images of the fire as "some of the most frightening stuff" he's seen.

"The strength of the wind, and the dryness of it and the conditions over the weekend - it is miraculous that we're here this morning talking about no homes lost," he said.

Concerningly, the fire is getting close to the Lucas Heights nuclear reactor.

"Australia's only nuclear reactor is right bang smack in the middle of it, so that adds another dimension.

 "You've got a military base there too where there's live active firing and artillery kept in that area."

Morrison said there were still about 100 firefighters responding to the inferno, which they were finally bringing under control.

"They do believe that temperature-wise and condition-wise, the worst part's behind them."

There were reports on Monday morning that some properties had been affected, but it's not known how many.

Police suspect the blaze was deliberately lit.