Tennis is a big talking point in Auckland at this time of year, as fans flock to the central city ASB Tennis Centre for the annual ASB Classic.

The two-week-long tournament comprises of a WTA 250 event and an ATP 250 event.

Draws for both hard court tournaments consist of 32 players.

While organisers aren't disclosing attendance figures, 1News understands tens of thousands attended games last year and this year's figures would set new records.

Four time Grand Slam Champion Naomi Osaka is through to the quarter finals on Thursday. Top seed Madison Keys is through to the Round of 16.

Naomi Osaka spent an hour on the practice court this morning with Coach Patrick Mouratoglou and her hitting partner.

Keen tennis fans are turning out early to training and warm-up sessions, and some spectators at the practice told 1News they enjoyed the quality hitting and dedication Osaka brought to training.

There were also a number of activities in the Fanzone including the opportunity to learn "Pacific Padel" – a racket sport popular in Europe.

Behind the scenes and out on court 350 volunteers ensured the event ran smoothly. Tasks included driving players to and from their games, on-court ball kids, mopping the courts dry after rain and ensuring fans get to their seats before play commences.

Last year the tournament brought 16,600 visitor nights to the host region, and injected $3.4 million into the local economy.

Broadcast numbers last year were also the highest on record, with an increase on both domestic reach and viewer hours.

The International broadcast saw a global audience of more than 12 million with the top markets outside of NZ being the US, Lat Am, Pan Asia and Serbia.

The women's tournament concludes with the final on Saturday, January 4.

Qualifying for men's tournament would also get underway on Saturday, with the final scheduled for January 11.