(AFP) - Caroline Wozniacki and Ana Ivanovic will compete at the Auckland Classic in January, organisers said on Wednesday (Nov 23), hailing "the strongest field ever" at the Australian Open warm-up tournament.

With Serena and Venus Williams' participation previously announced, tournament director Karl Budge said there would now be four former world No. 1s lining up in New Zealand.

"This is uncharted territory for a sporting event in New Zealand," he said.

"Any one of these four players could headline the tournament on their own. They are the most marketable female athletes in the world."

Wozniacki, currently ranked 19th in the world, and Ivanovic (63) are both on the comeback trail after battling injuries.

"I have very fond memories of winning the title in Auckland 2014 and I am determined to make my mark again in 2017," Ivanovic said.

Venus Williams (17) won the event in 2015, beating Wozniacki in the final, while world No. 2 Serena has never played in Auckland.

Defending champion Sloane Stephens (35) of the USA is also part of the 24-player field.

The tournament runs from Jan 2-7 in the lead-up to the season's opening Grand Slam in Melbourne that begins Jan 16.