An important New South Wales the highway reopened after black ice closed it for hours amid a late winter snowfall.

The Great Western Highway was closed between Katoomba and Mount Victoria this morning, seeing traffic pile up for hours. Truckers even turned off their engines and went out to play in the snow, with no predictions about when the road would reopen.

The Transportation Management Center confirmed the freeway reopened in both directions around 10:20 a.m.

Endangered Creatures at Home in a Late Winter Wonderland

The Great Western Highway in New South Wales has been closed due to black ice. (9News)

Bells Line of Road, another thoroughfare in the Blue Mountains, has now also reopened between Lithgow and Bell.

People are advised to give themselves extra travel time. Blue Mountains trains also remain delayed.

Temperatures dropped 10C in just two hours across Sydney overnight, driven by a sudden change in the southerly wind bringing a very cold air mass.

Traffic has been greatly slowed down. (9News)
An icy front brings freezing temperatures to NSW and Victoria. (9News)

In Katoomba, west of Sydney, it hit -1.5C but felt like -7C, resulting in snowfall covering the ground.

More snow fell in parts of Victoria days into spring on September 1.

Meanwhile, a severe weather warning is in place across New South Wales today.

Snow fell in the Blue Mountains overnight. (9News)
Kangaroos in the snow on a property between Berridale and Jindabyne in NSW.
Kangaroos in the snow on a property between Berridale and Jindabyne in NSW. (Phil Richmond)

Dangerous surf and swells are expected along the coast from Byron Bay to Illawarra.

Residents are advised to stay out of the water.

The cold front that brought snow and freezing temperatures has already moved offshore, meaning the weather will not stick.

Snow showers in Bathurst on Tuesday August 23
Snow showers in Bathurst on Tuesday August 23 (Provided)
Snow in the Victoria area on Tuesday August 23rd.
The Victoria region also had a few falls. (9News)

But today Sydney and much of NSW can brace for a very cold and windy day.

In Melbourne, the weather will likely be similar, with a chance of rain in the afternoon.