With most of the world still living under strict coronavirus restrictions, there is some light relief for tennis fans in the form of a very different Australian Open.

Serbia's world number one Novak Djokovic and Spain's Rafael Nadal - who is aiming to win a 21st major title and move clear of Roger Federer - lead the men's field.

Another all-time great, Serena Williams, headlines the women's tournament. The American launches another attempt to land that elusive, record-equalling 24th Grand Slam singles title.

From a British perspective, there is no Andy Murray, with Johanna Konta and Dan Evans leading the nation's hopes.

But it is a tournament that has been mired in controversy.

Held in a country imposing some of the toughest coronavirus restrictions in the world, many Australians argued it should not be played at all.

Months of strict border controls have helped Australia limit Covid-19 cases to fewer than 29,000 and deaths to fewer than 1,000.

Australian player Nick Kyrgios said he could understand any sense of uneasiness over 1,200 players and support staff flying in from overseas.

"Whether or not it's the right time, that's not for me to say because we are going ahead with it," the world number 47 said.

"But I think sport is essential for us. Especially with tennis having such a rich culture in Australia, I think we almost need it in a sense.

"I think as long as everyone follows the protocols then it's OK. We all need to stay the course with everything to make sure it doesn't take off again, because the reality is it's killing people and it's not a game."

Is it a fair competition?

In order for the tournament to take place, Australian Open bosses had to agree an unbending policy with the Victorian state government over the arrival of the players.

That meant those travelling had to test negative before taking a charter flight to Australia in mid-January, then undertake a 14-day quarantine period where they could only leave their room for five hours each day.

However, stricter restrictions were imposed on 72 players - including British number two Heather Watson - after positive Covid-19 cases were found on three of the charter flights bound for the tournament.

Those players were confined to their rooms for 14 days, unable to go out to practise like their rivals and left having to think of novel ways to keep sharp indoors.

In order to warm up the players for the Grand Slam, six tournaments have taken place simultaneously at Melbourne Park this week - including a specifically arranged event solely for those WTA players in the hard quarantine.

There was further disruption this week when 160 players were told to isolate, pending a negative coronavirus test, after a security guard at the hotel where they were quarantined tested positive.

"Everyone is really playing it by ear. Nobody really knows who is in form and who is not," added Kyrgios, who competed for the first time in almost a year in one of the warm-up events.

There was further discontent among some players about the star names - including Nadal, Djokovic, Williams and US Open champion Naomi Osaka - spending their quarantine period in Adelaide instead of Melbourne.

While they too were only allowed out of their rooms for five hours as per the quarantine rules, there was bristling at a perceived preferential treatment and accusations they had an unfair advantage.

French doubles player Edouard Roger-Vasselin said there was a feeling those players had "more time to prepare and more time to practise."

"Over 14 days that could be a big difference between these players and the rest of the group," he added.

Australian Open tournament director Craig Tiley said the top players were sent to Adelaide to ensure organisers did not exceed the limit set by the authorities for people quarantining in Melbourne.

Can the returning Barty finally end Australia's wait?

Home hopes of a first Australian Open champion since 1978 are pinned on Ashleigh Barty.

The 24-year-old Queenslander is still ranked as the world's leading player, despite not having competed for 11 months before this week's Yarra Valley Classic.

Three wins in the tune-up event set up a semi-final against Serena Williams, with Barty progressing to Saturday's final when the American great withdrew because of a shoulder injury.

"The rust is always there for, I think, everyone the first few matches of the season. But without a doubt, I felt better and better each match," said 2019 French Open champion Barty.

As ever, the spotlight will also fall on Williams, who is seeded 10th. Without a major since the 2017 Australian Open title, the 39-year-old is aiming again to match Australian Margaret Court's all-time leading tally of singles victories.

Another American, Sofia Kenin, is expected to provide a strong defence of the first Grand Slam title she won in Melbourne last year, while Polish 19-year-old Iga Swiatek goes in as the newest major champion after beating Kenin in the French Open final in October.

While there is little form guide, 2019 champion Naomi Osaka has looked sharp this week and picked up where she left off last year when she won the US Open.

A string of injury problems have stalled the progress of Canada's Bianca Andreescu since her victory at the 2019 US Open, with the 20-year-old hoping to put them behind her when she plays for the first time in 15 months.

British number one Konta, a Melbourne semi-finalist in 2017, will be seeded 13th.

Will Nadal win his 21st major? And can Djokovic be stopped at his second 'home'?

Serbia's defending champion Djokovic headlines the men's singles at an event where beating him has proven extremely difficult in recent years.

The 33-year-old's triumph last year was a record-extending eighth title at Melbourne Park, where he has won his past 14 matches and lost just four times in the past 10 years.

Consequently, he is the favourite to win a 18th Grand Slam tournament at a place he says "feels like home".

"Each year that I come back to the court, it feels even better. The more you win obviously on the court, the more confident you feel coming back to it," said the world number one.

Also expected to challenge is Nadal, although he has been nursing a back injury this week.

The Spanish second seed is aiming to move clear of great rival Roger Federer - who is absent through injury - in terms of most men's majors after claiming a record-equalling 20th title at the French Open in October.

Austrian third seed Dominic Thiem, who lost to Djokovic in last year's final, is another contender. The burden of a first Grand Slam title is now behind the 27-year-old after winning the US Open in September.

Russia's Daniil Medvedev is likely to threaten too, while Greece's Stefanos Tsitsipas and Germany's Alexander Zverev are attempting to better their runs to the semi-finals in recent years.

British number one Evans, seeded 30th, warmed up by reaching the semi-finals of the Murray River Open at Melbourne Park.

Six-time champion Federer, 39, misses the tournament for the first time in his career as he continues his recovery from knee surgery.

Meanwhile, Andy Murray saw his plans disrupted after more rotten luck in what has been a testing few years for the British former world number one.

Murray, a five-time runner-up, was unable to fly out to Melbourne as planned after testing positive for coronavirus.

After seeing his career derailed by a serious hip injury, the three-time Grand Slam champion has now missed nine of the past 13 major tournaments going back to Wimbledon in 2017.