Homes lose power and crews respond rapidly to grassfire at Goulburn's Kenmore Hospital

Residents surrounding the Taralga Road facility reported an "alarming" large bang, a power outage and then smoke and flames at about 9.30pm Sunday.

NSW Fire and Rescue captain, Chris Corcoran, said two crews and four RFS brigades responded to the fire. It broke out beneath power lines between the old sporting fields and Wollondilly River in the vast complex.

"Firefighters faced two metre high flames on arrival," Mr Corcoran said.

The blaze broke out in waist-high grass, opposite the sporting fields and burnt through 2.5 hectares, towards the river.

The fire was away from buildings and no structures were destroyed.

Mr Corcoran said it did not blow an electricity transformer, as some had suggested.

"I'm not sure why there was an explosion - whether it was arcing powerlines or wildlife on the lines, we're just not certain," he said.

The cause is being investigated but is not believed to be suspicious.

Police attended as a matter of course.

An Essential Energy spokeswoman said the provider turned equipment off at 9.43pm for safety. Crews restored power to 82 customers one hour later and a further 47 by 11.26pm.

The transformer was not damaged. The spokeswoman said no fault was determined.

Mr Corcoran said while grass was long throughout the complex, it was evident caretakers had previously slashed it as a fire prevention measure.

The blaze came on an extreme fire condition day and a total fire ban. Mr Corcoran said authorities weren't taking any chances and pounced on it quickly. It was brought under control within an hour.

The fire also came after another in October, 2021, which extensively damaged the former female ward 15 on the Kenmore site. More than 30 firefighters responded to the three-storey building fire. Two youths were later dealt with under the Young Offenders Act for deliberately lighting it.

In response, Heritage NSW issued the owners with several compliance orders and ordered that security fencing be erected around the complex.

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