About 11,100 residential and business customers on Sydney's north shore and northern beaches remain without electricity on Friday evening following Tuesday's severe storms.

Residents have been warned the outages could continue into the weekend.

Utility company Ausgrid 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, and claimed the workforce of 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 simple fact is that the number of crews available directly impacts the speed that repairs can take place.

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

Mr Page said crews were stretched even before this week's storms due to the unprecedented bushfires burning across NSW.

The union boss called on the federal and state governments to overhaul the "flawed" Australian Energy Regulator (AER), which he blamed for huge cuts to the NSW electricity network in recent years.

"With extreme weather events such as storms and bushfires predicted to become more common with climate change, the prudent course of action would be to ensure staffing levels take these risks into consideration through increased frontline resources and investment in making the power network more resilient," he said.

But AER chairwoman Clare Savage said while the regulator determines revenue for distributors, it does not have responsibility for staffing levels.

"The business is responsible for deciding how they spend those revenues - delivering the services consumers require while meeting their legal obligations on safety and other issues," she said.

"Staffing levels are a matter for the business, not the AER."

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

The company on Friday said it had restored power to 39,000 customers, including 2000 overnight.

But 11,100 customers in the hardest-hit areas are still without power and that situation could continue into the weekend.

NSW Police has opened the Public Information and Inquiry Centre in relation to the outages, saying some properties would not get power back until at least Sunday.

Members of the public were asked to look out for those who might need help.

The company said 700 people - including extra Ausgrid crews from Newcastle and the Central Coast as well as teams from other distributors - are working to get people back on the network.

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.

Crews have been called in from as far as Penrith and Wollongong, and the teams are rotated to manage fatigue.

The SES has had more than 2300 calls for assistance since Tuesday but it's anticipated it will wrap up operations within the next day or two.

At the height of the storms - which downed trees and powerlines in Sydney - 52,000 customers were without electricity.

Australian Associated Press