A woman has denied sabotaging gas supplies at a major public hospital after revelations a man died an hour after the alleged tampering.

Officials have launched a major investigation after it was confirmed on Wednesday that a 72-year-old died at a hospital in Sydney’s south early the previous morning.

The man died about an hour after Vanessa Moulton, 42, allegedly turned off medical gas supplies at Sutherland Hospital, forcing the facility to switch to portable oxygen and air for two hours.

Just after midnight she also allegedly cut the gas and water mains at the nearby Kareena Private Hospital at Caringbah before setting off the fire hoses.

Moulton appeared in Sutherland Local Court on Wednesday morning on a string of charges, including sabotage, destroying or damaging property and custody of a knife in a public place.

She also faces charges of tampering with a fire alarm and trespassing over a separate incident at a hostel in inner-city Darlinghurst on Monday.

The NSW government initially said the outage at Sutherland Hospital did not impact patient care, but Health Minister Ryan Park said he had since been made aware of the man’s death.

“This morning, I phoned the family to extend my deepest condolences,” he said.

A death certificate had initially been issued, but the coroner and police were later called in to investigate.

“I want to assure the community that the full force of the law will be applied,” the minister said.

Moulton has not been charged in relation to the man’s death and it is not clear if it is directly linked to the gas tampering.

A security audit of critical hospital infrastructure is expected to begin with the government flagging a major investigation into the incident.

NSW Premier Chris Minns said he wanted to assure patients and families, as well as workers who rely on the infrastructure, that everything would be done to keep it safe.

The man’s family would be provided as much information as possible, he said.

The local court heard Moulton had failed to report to police on Monday as required under her bail conditions for separate charges.

“I thought it was Sunday not Monday,” the 42-year-old said in response after repeatedly declining the offer of legal representation.

When asked by magistrate Pilar Lopez why her detention on the charge of sabotage, which carries a maximum jail term of 25 years, was unjustified, Moulton replied: “I didn’t do it.”

She was remanded in custody to return to court on December 24.

A spokesperson for Ramsay Health Care, which runs the private facility, said all its hospital’s services were quickly restored with minimal disruption and no impact to patient care.

Sutherland Hospital has 375 beds, while Kareena Private Hospital is a 142-bed facility.

–AAP