Don't let the clear skies and sunshine fool you - it's Sydney's coldest morning in a year.

Just before sunrise, Sydney's Observatory Hill recorded a temperature of 5.5 degrees, which is 2.5 degrees below average, weatherzone.com.au senior forecaster Alex Zadnik said.

Mr Zadnik said it had not been so cold since June last year, when a minimum of 4.3 degrees was recorded.

Sydney's suburbs shivered through temperatures below zero just before 7am.

It was -2.1 degrees in Camden, -2 degrees in Campbelltown, -2 in Richmond, -1 in Bankstown and -1.8 in Holsworthy.

"The chilly conditions were the result of easing winds and clear skies in the wake of the cold front that brought the strong winds to Sydney over recent days," Mr Zadnik said.

He said the air mass following the cold front was dry, which caused a rapid loss of heat.

The Bureau of Meteorology said there would be areas of frost in Sydney's west this morning, with a maximum of 16 degrees in the city.

About 4000 homes in the Blue Mountains, southern highlands and Shoalhaven are still without electricity, but an Endeavour Energy spokesman said crews were aiming to restore power to most of those properties today.

Some outlying areas will have their power restored over the weekend.

Plenty of Sydneysiders tweeted about waking up to the chilly weather.

"In all the 2 years I've lived in sydney, the winter has never been this cold. Brrrrrrrr freezing," one person wrote.

Another wrote: "I can't remember #sydney ever being this cold."

Weatherzone.com.au is owned by Fairfax Media, publisher of this website.

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