Tennis star Serena Williams put up a signed dress, worn at her first tournament of the year, for auction to raise funds for firefighters tackling Australia's unprecedented bushfire emergency.

Williams, who is preparing for this month's Australian Open at the WTA Auckland Classic, joins a slate of sports stars from around the world who have stumped up memorabilia and cash to help pay for firefighting efforts.

"I have so many friends in Australia and it's just been really tragic all around," the 23-time Grand Slam champion said on Friday.

"I just keep asking every day to people back home or in Australia, what can I do? Is there anything I can do? It's literally devastating for me and I'm sure a lot of other people feel the same way."

Her outfit, listed as "a bespoke Nike dress made specifically for Serena", was worn by the American when she beat Italy's Camila Giorgi in the first round at Auckland. Williams progressed to the tournament's semi-finals on Friday.

Also for sale is a tennis ball signed by Williams and Caroline Wozniacki, as well as a one-hour private training session from Serena's long-time mentor Patrick Mouratoglou.

The auction closes at midday Saturday (2300 GMT Friday).

Read more: Cricket legend Warne's cap raises Aus$1m for bushfire appeal

Earlier on Friday, Australian cricket legend Shane Warne raised more than Aus$1 million (nearly $700,000) for bushfire victims by auctioning off the "baggy green" cap he wore through his Test career.

It came a day after reigning Formula One champion Lewis Hamilton pledged $500,000 for relief efforts, saying that he had been deeply saddened by reports that over a billion animals had been killed in the fires.