Wind gusts topping 100 km/h on Sydney Harbour and Botany Bay - the strongest in more than a year - knocked out electricity to tens of thousands of residences on Friday, and stranded northbound trains on the harbour bridge during the middle of the day.

The Bureau of Meteorology maintained a severe weather warning across much of eastern NSW, with wind speeds expected to pick up again around sunrise on Saturday.

Winds "will still be pretty strong but not as severe" on Saturday, Ashleigh Lange, a bureau meteorologist, said, adding wind gusts should reach as much as 70-80 km/h across Sydney during the day.

Those winds may ease back to light conditions only by Sunday afternoon.

Turbulent weather may trigger further delays on Saturday at Sydney Airport. Dozens of flights were cancelled or delayed on Friday with domestic services bearing the brunt of disruption.

A separate warning for large and powerful surf conditions for the NSW coast is also expected to be in place until at least Sunday. Waves could top six metres, eroding exposed beaches.

"These strong winds have picked up a huge swell," Ms Lange said.

A combination of a deep low in the Tasman and a big high-pressure system moving in from the west created the sharp pressure gradient that generated the strong winds, she said.

Sydneysiders might have thought they were in Melbourne or points further south with the wind chill briefly dipping below the zero-degree mark near the height of the winds. The 106 km/h gales on Sydney Harbour were the city's strongest since June last year.

"Feel like" temperatures are likely to feel barely warmer than freezing for much of Saturday, although the official top will nudge 16 degrees. Sunday's maximum for Sydney will be about 17 degrees after a chilly 7-degree overnight minimum, the bureau predicts.

"We have some really cold air moving through," Ms Lange said.

Traffic and power were both disrupted by falling trees, especially in the city's south with Ausgrid battling to reconnect more than 40,000 homes and businesses at one point on Friday.

The T3 Bankstown Line was one of the lines briefly disrupted by the winds, with a tree falling across the tracks on Friday afternoon.

Amid the chaos, authorities had to tackle bushfires, such as at Anna Bay, and have had to curtail some planned hazard-reduction burns for this weekend.

Fire crews also had to cope with blazes near Sydney Harbour.

During the clean-up to come, engineers will examine a range of buildings that didn't cope well with the powerful winds.

These include Barangaroo, which shed some glass panels, and the Caringbah building in the Illawarra, which lost part of its roof.