Experts from the Bureau of Meteorology believe it "highly likely" a tornado is responsible for some of the damage delivered on the seaside holiday town during a severe weather event overnight Saturday.

The visiting bureau team will apply the Fujita scale, a measure of tornado intensity based on the amount of damage to homes and other structures.

Julie Evans, a meteorologist with the bureau, said it had been difficult to be certain of a tornado because the storm occurred at night.

"While some of the damage appears to be associated with very strong winds funnelling around the local hills and headlands, there is also a narrow path of damage consistent with a tornado," she said.

"It would appear that small-scale circulation formed within the sharp trough that was moving down the coast, bringing very heavy rain to the NSW coastal districts.

"It was dark - without visual observation of a funnel we cannot be conclusive, but it is highly likely that a tornado formed within that circulation."

The bureau has consulted State Emergency Services over the weather event and has looked to radar imagery and high-resolution wind data from its Kiama weather station in a bid to categorise what happened.

The tornado, if that is what it was, occurred as part of a band of very strong winds and rain.

The same weather system affected Sydney, with official data showing the highest gusts in the state were recorded at 135km/h in Sydney harbour about midnight.

The Kiama weather station - located at Bombo Headland - seemed to register the storm's arrival about 3.14am, recording 84km/h winds, but the station is located about a kilometre north of where far gustier tornado activity is thought to have occurred.

"This [84km/h] would be lower than the maximum experienced in the area," Ms Evans said.

Bureau personnel will take into account the types of buildings damaged as part of their assessment. Damage to a timber shack, for instance, would indicate a weaker tornado than damage to a newer, double-brick home.