An icy polar blast sending temperatures plummeting across New South Wales and the Australian Capital Territory is set to break records, as an east coast low heads for the coast.

June has been the coldest first month of winter in nearly 20 years for some parts of NSW, while Canberra is headed for its coldest run of nights in June in living memory experts say.

Weatherzone reports Canberra's minimum temperatures have averaged just -2.5 degrees for June and the final days of the month are looking to be just as frosty at below -3 degrees.

The combined average of minimum and maximum temperatures in the nation's capital reached just 5 degrees for June, making it the coldest June since records began in 1939.

Cooma in NSW's south has also experienced a run of bitingly cold nights.

Average minimum temperatures at Cooma Airport sank to -3.5 degrees, the coldest June minimum temperature since 1991.

Goulburn followed closely behind with an average combined temperature of just 6.2 degrees, only marginally warmer than Canberra, for the month of June.

The final night of the month is expected to be similarly cold, with average temperatures not expected to get any higher as records look to be shattered.

From tomorrow, cold conditions are expected to ease over NSW's east coast thanks to a humid easterly airstream developing offshore.

It will however remain cold across central and western NSW.

Minimum temperatures in Canberra are forecast to stay icy late next week, plummeting to -4 degrees on Friday and Saturday.

Melbourne is expected to be slightly warmer than its east coast counterparts with temperatures headed for tops of 15 degrees by Saturday.

Fresh warning ahead of east coast low

The wintery blast will bring gusts of up to 100km/h, forecasters say, with rainfall totals reaching 300mm possible in some areas, potentially causing flooding.

The BOM has issued a warning for flash flooding, coastal erosion and storm damage from Coffs Harbour to Bega in NSW.

Widespread rainfall of 50 to 100mm is likely, with isolated rainfall totals of 150 to 200mm possible.

"Intense" winds of up to 125km/h are forecast along the coast.

NSW SES Acting Assistant Commissioner Allison Flaxman ESM said there's a risk of damage from destructive winds and flash flooding.

"People should prepare now by tying down any loose items around their homes so they don't become projectiles and damage property in the forecast wind," she said.

Acting Assistant Commissioner Flaxman said the NSW SES has pre-deployed assets and volunteers to high-risk locations and would continue to work with the BOM on the latest forecasts.

"NSW SES teams have been monitoring this system for a week, and we have high clearance vehicles, aviation assets and personnel positioned in areas expected to be impacted ahead of the forecast weather," she said.

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