A woman is in police custody as officers investigate the cutting of essential medical gases at two Sydney hospitals, in what the state's health minister has called "deliberate sabotage".

NSW Police said a woman allegedly entered the hospital grounds of Sutherland Hospital in Caringbah about 12:20am and cut both the water and gas mains, before she turned on the fire hoses.

Police said about an hour later a woman the went into a private hospital on the same street and switched off the gas supply.

Health Minister Ryan Park said the public hospital had to rely on portable oxygen and air as part of its contingency plans.

Just before 4:00am a 42-year-old woman was arrested at nearby Miranda for alleged breach of bail and was taken to Sutherland Police Station for questioning.

A short time l

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