Thousands grin and bare it for swim at crack of dawn

Thousands of people have grinned and bared it for an annual nude mid-winter swim in Hobart, on the city's coldest morning of the year.

Towels were dropped when the sun rose at 7.42am on Monday at Long Beach for the dip which marks the winter solstice and end of arts and food festival Dark Mofo.

Lifelong friends Di Webb and Lorette Mansfield made the trek from Sarina in central Queensland.

It was Ms Webb's 60th birthday, while Ms Mansfield had celebrated her 61st on Sunday.

"Lorette lost her husband last year and we said 'let's do it'. It was just a bit of a support for her," Ms Webb said.

"(The water) wasn't as bad as I thought. Just invigorating. We ran straight in."

The temperature of the River Derwent was in the low teens, while the outside temperature was a much more nippy 4C.

Drumming was used to count down to sunrise, before red flares we lit and shrieks filled the air as the hardy souls hit the water.

Some were in-and-out, while others made it to offshore pontoons more regularly used in summer.

The 3000 tickets were quickly snapped up for the free event, which increased its capacity a few years ago.

Delyce Barba, who drove down from Launceston in northern Tasmania for her second swim, said she viewed the solstice as a chance to reset.

She went "up to the tits" before making her way back to the sand and also had some pointed pre-swim advice for the group she was with.

"I just said it's going to be f****** cold. They were terrified this morning. But they were great," she said.

Cath Lim, who hails from Queensland, jumped in for the first time as part of about half a dozen people who arrived in green frog onesies.

"I loved it. My mum and her friends have come and I said 'one year'. No regrets," she said, adding it got better the longer she stayed in the water.

The swim has been running since 2013 - the inaugural event of about 300 people almost didn't go ahead after police threatened to make arrests for public indecency.

In recent days Australia's Antarctic expeditioners have also celebrated the winter solstice, the shortest day and longest night of the year, with a swim.

Ice holes were dug at Mawson and Casey Station, while expeditioners at sub-Antarctic Macquarie Island also got in on the fun.

"Questioning life choices that we're choosing to go into minus two degree water on a minus 20 degree day." Casey Station leader Justine Thompson said.

Hundreds of people also stripped off for a plunge in Canberra's Lake Burley Griffin on Sunday to raise money for charity.