Sydney is unprepared for a major blackout that could plunge Australia's largest city into darkness, according to New South Wales' chief scientist.

The warning has been issued regarding dangerous events which could be caused by illegal actions or weather events, resulting in prolonged blackouts which could last several days.

New South Wales chief scientist Mary O'Kane told the Daily Telegraph the consequences of such a blackout would be extreme.

Sydney is unprepared for a major blackout that could plunge Australia's largest city into darkness, according to New South Wales' chief scientist

'For this reason, we've suggested all sorts of things be tested,' she said.

An Energy Security Taskforce led by Ms O'Kane gave a report to the state government on Tuesday warning a blackout would negatively impact fuel supplies, water quality and health care.

NSW Energy Minister Don Harwin said the state government has developed a 'strategic plan' for a response to a 'large-scale outage'.

The report said Sydney would most likely to be the last part of NSW to have power restored as it sits on the edge of the network.

There was also potential for sewage to overflow, and fuel and water supplies would drop.

Hospitals would need fuel delivered to power generators while healthcare records could not be accessed.

New South Wales chief scientist Mary O'Kane said the consequences of such a blackout would be extreme

Sterilisations may take up to three days to complete in such an event, while patients would need to be evacuated as air conditioning wouldn't work and the hospitals had fixed windows.

Trains would stop running, and up to 10,000 passengers would have to be evacuated from underground lines.

Electronic equipment connected to the NBN would no longer work and phones would be dependent on their battery life.

NSW Energy Minister Don Harwin said the state government has developed a 'strategic plan' for a response to a 'large-scale outage'

The report said the state needs a better plan for getting the power back on in a blackout.

Ms O'Kane said NSW was more prepared for such an event than it was a year ago.

'There is still risk of high demand during a heatwave, but in terms of how it will affect the state, we're in a better position,' she said.