The International Triathlon Union world triathlon series begins in Auckland at midday on Saturday. The course runs through the central city and 50,000 spectators are expected.
It is the third time Auckland has hosted a leg of the series which is held in eight cities around the world and ends in London in September.
Organising company chief executive Dave Beeche said people wanting to get to the event should use public transport because many roads will be closed around the central business district and the eastern waterfront.
A number of bus stops will be temporarily relocated and representatives will be at most stops to help passengers.
All streets will reopen by 5pm on Sunday.
