An elderly man has died after a woman allegedly cut essential gas services to two Sydney hospitals.

Vanessa Joy Moulton, 42, allegedly disrupted critical gas and water supplies at Kareena Private and Sutherland hospitals in Sydney’s south early Tuesday. 

Police rushed to Kareena Road in Caringbah, 24km south of the CBD, about 4.20am following reports of vandalism at two hospitals on the same street.

Police allege the gas and water mains were cut at Sutherland Hospital just after midnight before the fire hoses were activated.

The hospital was forced to switch to portable oxygen and air for two hours after it lost gas supplies. 

About an hour later, Moulton allegedly walked across the road and switched off the gas main at Kareena Private Hospital.

Police were later told on Tuesday that a 72-year-old man died at Sutherland Hospital at about 2.30am that morning.

Doctors issued a death certificate and a report will be prepared for the Coroner.

Moulton was arrested on Parkside Avenue in Miranda on Tuesday morning for breach of bail.

She has since been charged with two counts of public nuisance, two counts of trespassing, sabotage, and destroy or damage property and breach of bail.

Moulton was also charged with tampering with fire alarm or fire signalling apparatus, and trespass on protected premises in relation to a separate alleged incident at a Darlinghurst hostel on Monday.

No charges have been laid over the death of the hospital patient. 

Moulton appeared in Sutherland Local Court videolink on Wednesday, where she was refused bail. 

She declined the assistance of Legal Aid and was asked by the magistrate why she should not remain in custody.

‘I didn’t do it,’ Moulton replied, NCA Newswire reported.

She will remain in custody until her next court appearance at the Downing Centre on December 24.

NSW Premier Chris Minns said that the man’s death will be ‘fully investigated’.

‘We want to make sure that the family has as much information as we have and that we communicate it to them as soon as possible,’ he said on Wednesday.

He added that critical hospital infrastructure statewide will undergo a thorough security audit.

‘It’s such a shocking allegation it may well have been the case that it was believed that no one would be so callous or cruel,’ Minns said.

‘We’re obliged to protect that critical infrastructure and I want to assure patients and families across NSW Health, as well as the workers that rely on that infrastructure to work, that we’re going to make sure that we do everything we can to keep it safe.’

There was no impact to patients from the alleged tampering of mains water and non-medical gas supply at Kareena Private Hospital.

‘All services were quickly restored with minimal disruption and no impact to patient care,’ a Ramsay Health Care spokeswoman said.

Earlier, NSW Health Minister Ryan Park said the act of alleged ‘sabotage’ could have had ‘catastrophic’ consequences for more patients.

‘It is very, very concerning that life-saving medical gases have been [allegedly] sabotaged at the public and private hospitals,’ he told reporters on Tuesday.

‘Access to gas systems in NSW public hospitals is restricted and we will review the incident to see what improvements can be implemented.’

Health Services Union secretary Gerard Hayes called for a review of hospital security resources.

‘The threats facing our hospital security are greater and more unpredictable than ever before, yet the resourcing is simply not keeping up,’ he said.

‘It’s clear that protecting critical infrastructure like medical gas systems must be a priority.’