Network operator Ausgrid said 700 crews were working to replace severed lines and broken poles from Tuesday's severe storms, but warned customers to "prepare to outages lasting well into the weekend".

"We saw cyclone type storms - it was quite exceptional even though they lasted about 10 minutes," a spokeswoman told AAP on Saturday.

By 10pm, 4600 residential and business customers in Sydney's northern suburbs remained without electricity.

Power had been restored to more than 47,000 customers since Tuesday.

Further complicating the issue, Ausgrid said it had come across many homes where individual customers' connections to the network - such as private power poles - had been significantly damaged.

Ausgrid said regulations prevented its staff from repairing customer equipment past the connection point, and urged those affected to contact a qualified electrician to repair damage to their own equipment.

"Once repaired, Ausgrid can safety reconnect them to the shared network," a statement on Saturday said.

NSW Police opened an information and inquiry centre for the outages, asking people to check on friends or neighbours in affected areas who "might be vulnerable and in need of assistance".

Ausgrid previously said the cyclone-like damage was some of the worst it has seen in a concentrated area.

But the Electrical Trades Union said the length of the large-scale blackout highlights the impact of job cuts, claiming the workforce at NSW's three electricity distributors had been slashed by 40 per cent.

"Ausgrid alone has seen approximately 2000 jobs go with another 315 people made redundant earlier this year," union secretary Justin Page said in a statement.

The number of crews available directly impacts the speed of repairs, he said.

"If you have a much smaller workforce, the time the public is left without power greatly increases," Mr Page said.

Ausgrid has been contacted for comment on the union's claim.

People relying on a continuous power supply for medical or life support equipment have been advised to relocate.

State Emergency Service regional operations director Paul Bailey said crews were doing "absolutely everything they can" to clear affected areas.

"I do understand these are very trying circumstances for people - being without power is a very difficult thing and I know that everybody is doing their best to fix that," Mr Bailey told reporters in Sydney.

Australian Associated Press