Serena Williams left her Australian Open news conference in tears after her semi-final defeat by Naomi Osaka.

She gave the crowd inside Rod Laver Arena a long wave goodbye with her hand over her heart, leading to questions over the 39-year-old's future.

She responded: "I don't know. If I ever say farewell, I wouldn't tell anyone."

Williams became tearful when asked a further question about her unforced errors against Osaka.

"I don't know. I'm done," she said, before leaving the room.

Williams thanked her fans in a post on Instagram shortly after the match.

"Today was not ideal outcome or performance but it happens. I am so honoured to be able to play in front of you all," she wrote.

"Your support, your cheers, I only wish I could have done better for you today.

"I am forever in debt and grateful to each and every single one of you."

Williams has been aiming to equal Margaret Court's major record since her return from maternity leave in 2018.

Her 23 Grand Slam titles is the most by any player in the Open Era, with 13 of Court's titles coming before the tour became fully professional.

Since her return, Williams has reached four Grand Slam finals but lost them all, including to Osaka at the 2018 US Open.

It is the first time in 18 years that Williams has lost an Australian Open semi-final.

It is also her first loss against a top five opponent at a hard court Grand Slam since she was beaten by Jelena Jankovic in the Australian Open last 16 in 2008.