Defending champion Novak Djokovic admitted his Australian Open might be over after an injury-hit win on Friday as fans were kicked out ahead of a state-wide coronavirus lockdown.

In extraordinary scenes, the eight-time winner's night match against Taylor Fritz was suspended at 11:30 pm (1230 GMT) to clear Rod Laver Arena before Victoria state's six million residents were locked down at midnight.

The five-day lockdown, during which fans are barred and players go into a biosecure "bubble", follows an outbreak of the highly contagious UK coronavirus strain stemming from an airport hotel.

In the now-empty stadium, a grimacing Djokovic, who needed repeated treatment on an abdominal injury, recovered from losing the third and fourth sets to beat Fritz 7-6 (7/1), 6-4, 3-6, 4-6, 6-2.

After his roars of celebration echoed around the empty stadium, Djokovic said he didn't know if he'll be able to play his last-16 match against Canada's Milos Raonic.

"I know it's a tear, definitely, of the muscle so I don't know if I'll manage to recover from that in less than two days," said the Serb. 

"I don't know if I'm going to step out on the court or not, I'm just very proud of this achievement tonight.

"It was definitely one of the most special wins in my life," he said.

It was a brave effort from Djokovic, whose 17 major wins include 2012's epic, 5hr 53min Australian Open final against Rafael Nadal, the Open era's longest Grand Slam decider.

Earlier, Australia's Nick Kyrgios thrilled the crowd one last time before the lockdown but he succumbed in five set to US Open champion Dominic Thiem.

Thousands of fans, mostly unmasked, watched the flamboyant Australian throw away a two-sets lead as Thiem took it 4-6, 4-6, 6-3, 6-4, 6-4.

Fans booed public announcements telling fans to be home by midnight, while similar warnings were flashed up on the big screens.

The Australian Open, which has encountered severe coronavirus problems and started three weeks late, has been the first tennis Grand Slam to welcome fans in large numbers since the pandemic.

"It's rough. It's going to be a rough few days for everyone," said Serena Williams, who learned of the lockdown when she came off court earlier in the day.

Madame Butterfly

With 22,299 spectators on Friday, the best attendance so far, Williams and Naomi Osaka safely reached the last 16 along with fellow major-winner Simona Halep.

Williams survived an error-strewn performance to beat Russia's Anastasia Potapova 7-6 (7/5), 6-2 and set up an encounter with powerful Belarusian Aryna Sabalenka.

The 39-year-old American, tracking a record-equalling 24th Grand Slam title, dished up 31 unforced errors -- but was given a big helping hand by Potapova, 19, who hit five double faults when trying to serve out the first set.

Osaka was troubled by a butterfly that landed on her nose during an otherwise routine 6-3, 6-2 victory over Tunisian 27th seed Ons Jabeur.

"I felt like I wasn't playing that well, like my unforced error rate was probably really high today," said the Japanese star, who carried the insect to the side of the court before continuing. 

"But I'm really happy with how I fought."

Osaka's next opponent is two-time Grand Slam winner Garbine Muguruza, who continued her formidable form with a one-sided 6-1, 6-1 win over Kazakhstan's Zarina Diyas.

French Open champion Iga Swiatek, 19, who is seeded at a Grand Slam for the first time, beat France's Fiona Ferro 6-4, 6-3 to set up a meeting with Halep, a 6-1, 6-3 winner over Russia's Veronika Kudermetova.

And little-known Russian Aslan Karatsev, ranked 114, caused the biggest shock of the men's tournament when he upset Argentinian eighth seed Diego Schwartzman 6-3, 6-3, 6-3.

The 27-year-old, dogged by injury during his career so far, is yet to drop a set on his Grand Slam debut and next plays Felix Auger-Aliassime, who beat fellow Canadian Denis Shapovalov 7-5, 7-5, 6-3.