A global TV audience of 25 million is tipped to tune in for the Barfoot & Thompson World Triathlon series of events in Auckland.
A series of age group races and events will run throughout Labour Weekend, with the elite women's championship on Saturday and the elite men's on Sunday.
More than 7000 athletes are taking part from 60 countries and about 100,000 spectators are expected.
Special spectator grandstands have been constructed at Queens Wharf.
Triathlon grand final chief executive Dave Beeche said his organising team was "taking the sport to new frontiers".
"Auckland City and New Zealand can be proud of this achievement.
"We are, of course, as far away from the rest of the world as you can get, but despite the increased challenges that distance brings, we will set a numbers benchmark."
The races - which include juniors, under-23s, elite and teams - are taking place in downtown Auckland, forcing road closures and limited access around the CBD, Tamaki Drive, Parnell and North Wharf areas.
New Zealand Olympians Bevan Docherty, Kris Gemmell, Andrea Hewitt and Kate McIlroy are among 360 elite triathletes competing.
Gemmell was a top participant in the Auckland leg of the ITU World Cup series last November.
Gemmell won the Men's Elite event and Docherty finished second.
The event drew thousands of spectators as well as those who signed up to participate in what is the country's fastest growing sport.
The cream of the crop are not the only focus as 3000 age group racers (men's and women's under-19s and under-23s) will chase world titles and rankings on the final day of events on Monday.
Auckland Mayor Len Brown, who is at present overseas, said the event was another chance to show off the city on the world stage.
"It will be fantastic to have Auckland back on the world sporting stage.
"Queens Wharf was party central during the Rugby World Cup last year and now it's going to be triathlon central."
Mr Brown's first engagement when he returns to Auckland will be at the event's official opening ceremony, at Queens Wharf, tomorrow at 5pm.
25 million Estimated television audience
$7 million estimated economic value to Auckland
100,000 spectators expected.
Road closures and limited access around the CBD, Tamaki Drive and Parnell
Where to watch: Queens Wharf (tickets $10-$50)By Tony Ng