Czech Kvitova, seeded eighth, dominated a tie-break to win a tight first set, in which the roof was closed at 4-4.

The two-time Wimbledon champion, 28, controlled the second as Collins, 25, grew frustrated.

Kvitova won 7-6 (7-2) 6-0 and will meet Naomi Osaka in Saturday's final.

US Open champion Osaka defeated Karolina Pliskova 6-2 4-6 6-4 in the second-semi-final.

A vicious forehand winner sealed victory on Kvitova's first match point as she reached her first Australian Open final.

"This means everything, that's why I work really hard - to be in a final at a Grand Slam," she said.

"Finally, I made it deep into a major. Whatever happens in the final I am very happy."

The winner of the final will replace Romania's Simona Halep as the world number one.

Can Kvitova cap fairytale story?

Kvitova had not reached a Grand Slam semi-final since being attacked in a robbery at her home in December 2016.

Now the former world number two has the chance to cap a fairytale story by winning a third major title on Saturday.

The left-hander said she was "fortunate to be alive", requiring surgery on the hand which she predominantly plays with before returning to the sport five months later.

She has started this year superbly, winning a 26th career title in Sydney and extending her winning streak to 11 matches here in Melbourne.

But her big serve came under pressure first in the opening set, Collins - who had never won a Grand Slam main draw match before this tournament - taking a second break point with a brilliant dipping cross-court return for a 3-2 lead.

Kvitova hit straight back with a break in the following game as the American's service game dipped, leading to a 41% first-serve percentage at the end of the first set.

Following the roof closure at the end of the eighth game, Collins started to grow frustrated and had two heated discussions with umpire Carlos Ramos either side of losing the tie-break.

She seemed to lose focus in the second set, winning just 12 points - four on Kvitova's serve - as the Czech needed just 32 more minutes to wrap up victory.

Danielle Collins was unhappy when the net-cord sensor incorrectly beeped while she was serving

'I was happier than the fans about the roof closure'

The conditions were a key factor in the first women's semi-final as temperatures were expected to reach around 40C in Melbourne on Thursday.

The Australian Open has introduced a new extreme heat policy this year, with a heat stress scale now indicating when a break should be introduced and play being stopped.

If the index reaches four, then the players are allowed a 10-minute break between the second and third sets.

If a five is recorded, the tournament referee can decide to close the roof on Laver and suspend matches on outside courts.

Before the match, the index read 3.9 and meant the roof remained open.

But it became quickly apparent that the index was going to rise quickly during the match between Kvitova and Collins.

At the end of the eighth game of the first set, umpire Ramos announced the roof was going to be closed because the scale had hit five - leading to huge cheers from the crowd.

Kvitova, who has struggled in heat in the past, won eight of the next 10 games - plus the tie-break - on her way to victory.

"In the second set I was happier than the fans when the roof closed," Kvitova said.

"The first set I was very tired and making errors. I couldn't have a full swing and be more relaxed like I was before so I was glad my game came in the tie-break.

"I like playing indoors and I think that helped me a little bit."