Simona Halep survived a three-set thriller against Angelique Kerber on Thursday to set up an Australian Open final against Caroline Wozniacki, where the number one ranking will be on the line.

The Romanian said for a fleeting moment she thought "everything had gone" when facing two Kerber match points before battling past the former champion 6-3, 4-6, 9-7.

But the tenacious Halep stayed alive to put her number one ranking up for grabs in the showdown against the number two seed, with both desperate to win a maiden Grand Slam title.

"Definitely was very tough. I'm shaking now," said Halep, who saved the match points at 5-6 on Kerber's serve in the third set.  She confessed she wasn't sure how she did it.

"I don't remember, but I didn't think about the score. I just took point by point. I had actually two moments when I felt that the match was over," she said.

"I had no power anymore and everything is gone. I didn't give up, which meant a lot, and that's how I won the match."

Wozniacki beat unseeded Belgian Elise Mertens 6-3, 7-6 (7/2) after a late wobble when she was broken serving for the match at 5-4 in the second set.

"Halep, just like me, was down match-points early on in the tournament," said Wozniacki. "I think it's exciting because we're both playing for the number one ranking."

Saturday's final, which could be played in forecast temperature of up to 35 Celsius, looks set to be a gruelling do-or-die clash between two players known for their tenacity and court coverage.

"I respect her a lot, and I know it's going to be similar. I will have to run, so a very good rest after this match," said Halep of Wozniacki.

"I want to give my best ... and not think about the title. If it's going to come, it's going to come."

In a see-sawing contest, Halep sprinted into a 6-3, 3-1 lead before 2016 Melbourne Park winner Kerber, seeded 21, fought back.

The Romanian finally prevailed in 2hr 20min with her fourth match point to ensure a new name will grace the trophy.

"I tried to be calm today. It was a rollercoaster, up and down," said Halep. "If you don't give up you can win. I did it well. I am proud of myself."

In her match, Wozniacki almost let Mertens back in when serving for the win at 5-4, and seemingly in complete control.

Two double faults enabled the Belgian, in her first semifinal at this level on her Australian Open debut, to level at 5-5.

Serving to take it to a tiebreak at 5-6 Wozniacki then needed to save three set points before sealing the match in the tiebreak.

"It means so much to me," said the Dane after reaching her maiden Australian Open final and her first Grand Slam decider since 2014.

"I'm really happy and proud of how I've managed to turn things around when things weren't going my way and keep it up whenever it was going my way."

The final will be only the 17th time in Australian Open history that the number one and two seeds have met for the title -- first and second seeds have won eight times each.

The last time it happened was in 2015 when top seed Serena Williams beat second-seeded Maria Sharapova.