Deadly NSW storm will ease after midnight: forecasters

The wild storm battering Sydney and the Hunter region will begin to ease around midnight, providing some relief for residents who have endured 24 hours of ferocious wind and rain.

MetraWeather told 9news.com.au the storm had developed from a powerful low pressure system which had hung over coastal NSW since yesterday morning.

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"Strong winds and rainfall are expected to continue through Tuesday afternoon and evening – particularly for the Sydney and Hunter regions – maintaining similar intensity to what has been seen so far," meterologist Rob Davis said.

"Conditions will finally begin to improve before midnight, albeit slowly, as the storm will continue to live along the NSW coastline through Tuesday night but gradually weaken into Wednesday."

Houses have been destroyed and three people killed in Dungog, while people in Sydney, Illawarra and throughout the Hunter have been told not to leave home unless it is absolutely necessary.

Mr Davis said the strong winds battering the coast and the Hunter had been unusually long-lived.

"Wind speeds of this magnitude are typically brief, and do not occur over the same region for more than a single hour, let alone an entire day," he said.

Gusts have been recorded of over 100km/hr, while Sydney Airport recorded a peak gust of 96km/hr.

Mr Davis said the storm was comparable to the powerful winds and rainfall that lashed Sydney on October 14-15 last year.