Ferocious winds that tear roofs off buildings and houses continue to batter Sydney Friday afternoon, and power supply has been interrupted in many areas, affecting an estimated 5,000 Aussies.

The powerful winds struck around midday, and the Bureau of Meteorology (BOM) has recorded gusts at over 100km/h.

BOM has issued a severe weather warning for the city and the NSW coast, as wave heights are expected to go over 5m. The strongest gusts are battering the CBD, Botany Bay and the Illawarra south of Sydney.

SES said its office has responded to 80 calls for assistance along the NSW coast from Sydney down to the Illawarra region.

VIDEO: Students leave St Paul's Catholic College in Manly over strong winds

St Paul's Catholic College in Manly has been evacuated after a roof was torn off one of its buildings. (Watch the video below or see this fresh clip upload.) Nine News reported two students were slightly injured in the incident.

It was "a 50m by 20m section of roof" that got ripped off the building, NSW Fire and Rescue Superintendent Tom Cooper told ABC News.

Mr Cooper said they have received all sorts of calls for assistance due to the very strong winds.

"We have had everything from grass and bush fires to building fires, to lift rescues. There've been trees down, numerous wires down, wires arcing, trees on power lines... There've been motor vehicle accidents. You name it, we have had it today."

The strong winds are expected to maintain its strength overnight. BOM is calling on the public to remain alert and watch out for falling trees and flying debris. It is also advising homeowners to secure loose items around the house and cover those that need to be protected.

Emergency services have also received reports of yachts being displaced by the gusts of wind.

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