Nick Kyrgios faces being unseeded at a grand slam for the first time in more than three years as the Australian Open boasts its strongest field in memory.

The world's top 101 men and 102 women have all confirmed they will compete at next month's Open in Melbourne.

Romanian world No.1 Simona Halep heads up the women's field, with Serbian superstar Novak Djokovic the men's top seed and targeting a record seventh Open crown.

American great Serena Williams, ranked No.16, will make her highly anticipated return to Melbourne Park for the first time since winning in 2017 when eight weeks pregnant with baby Alexis Olympia, while world No.3 Caroline Wozniacki will be trying to defend her women's crown.

Superstars Rafael Nadal and defending champion Roger Federer, ranked second and third respectively, will be back, as will five-times finalist Andy Murray after a frustrating few years using his protected ranking of No.2.

Ten Australians, led by women's world No.15 Ashleigh Barty, and men's No.31 Alex de Minaur, have secured direct entry to the main singles draws.

Officials on Wednesday couldn't recall the last time both the men's and women's top 100 players would take part in the season-opening slam.

"It's an exciting time of year and we can't wait to welcome this exceptionally strong player field to Melbourne for Australian Open 2019," tournament director Craig Tiley said.

The depth of the men's draw, coupled with a disappointing end to his 2018 season, has left Kyrgios unlikely to be seeded at a major for the first time since the 2015 US Open in New York.

A quarter-finalist in Melbourne earlier that year, Kyrgios has been seeded in his past 11 grand slam appearances.

But the 23-year-old has fallen to No.35 in the world, three spots out of the seeding zone, before the Australian summer.

The only way he can gain some seeding protection for the 2019 Open - which starts on January 14 - is by defending his Brisbane International crown and hoping for some late withdrawals.

Otherwise the Canberran will be cast as the most dangerous floater in the men's 128-strong draw.

Despite boasting seven players in the top 50, Australia's only Open singles seed will be Barty and possibly de Minaur if he can defend semi-final rankings points in Brisbane.

After falling in the final round of qualifying last year, Bernard Tomic has earned direct entry to next month's main draw after an encouraging season highlighted by his fourth ATP title win in Chengdu in September.

AUSTRALIANS WITH DIRECT ENTRY TO AUSTRALIAN OPEN (prefix denotes ranking)

MEN

31-Alex de Minaur 35-Nick Kyrgios 38-John Millman 46-Matt Ebden 72-Jordan Thompson 83-Bernard Tomic

WOMEN

15-Ashleigh Barty 35-Daria Gavrilova 46-Ajla Tomljanovic 72-Samantha Stosur