About 25,000 households are still without power across Sydney and the Blue Mountains, after an intense burst of wild weather caused large blackouts yesterday.

Key points: Ausgrid said it had to clear more than 1,500 "hazards" before repairs could begin

Ausgrid said it had to clear more than 1,500 "hazards" before repairs could begin Some people in Gordon and Mount Colah have been told they could go a second night without power

Some people in Gordon and Mount Colah have been told they could go a second night without power Yesterday, wind gusts of about 90km/h were recorded in Sydney

Ausgrid spokesman Jonathon Hall said the damage from yesterday's storm resulted in the largest power outage the network had seen in recent years.

"Some of the damage we have seen to the electricity network is severe and that's even to our high voltage network as well," he said.

The main impacted areas are in Sydney's north, including the Lower North Shore and Upper North Shore.

Ausgrid said some customers in these areas should prepare for another night without power.

On Tuesday night, fallen trees toppled onto cars and homes in the suburbs of Gordon and Kilara, causing significant damage.

Ausgrid said it had to clear more than 1,800 dangerous hazards including fallen power lines before repairs could begin.

A tree branch tangled between power lines in Gordon. ( ABC News: Lily Mayers )

"Customers should prepare for another possible night without power as we rebuild damaged sections of the electricity network," Ausgrid said.



Mr Hall said traffic lights in some areas would also be impacted.

Yesterday, winds of about 90 kilometres per hour swept through Sydney.

It was so intense some residents described the storm, which hit Gordon and Kilara on the Upper North Shore the worst, as a "mini tornado".

The electricity provider said it was sourcing extra crews from Newcastle and the Central Coast to help restore power.

"All planned jobs on the network which don't relate to storms have been cancelled to allow crews to focus on the storm repairs," Mr Hall said.

This trampoline found a new home during yesterday's storm. ( Twitter: @marty386 )

Students from some schools in Sydney's north were told to stay home today after the wild storm damaged buildings and cut their power.

The NSW Department of Education said Karonga Public School and Lindfield East Public School were closed today.

Parents at Davidson High School and Mimosa Public School were told they could keep their children at home due to the clean-ups on school grounds.

The NSW State Emergency Services (SES) said it was still working through a large backlog of calls for help.

SES spokesman Andrew Richards said hundreds of its personnel were out cleaning streets along in the Northern Beaches and Upper North Shore.

"Our crews will be coming out and removing a lot of those trees from access, such as driveways and roads," he said.