Prime Minister Jacinda Ardern announced a sudden change in alert levels after two new community cases of COVID-19 emerged on Saturday.
Auckland has been instructed to move into alert level 3 and the rest of New Zealand to level 2 for seven days.
Aucklanders must stay in their household bubble, while gatherings of up to 10 people are allowed only in the case of weddings, funerals and tangihanga, and physical distancing is required.
For the rest of the country at alert level 2, gatherings beyond the 100-person limit will not be allowed under any circumstances.
As a result, several events throughout New Zealand have been cancelled.
Events cancelled February 28 - March 6
Ports of Auckland Round the Bays - Sunday, February 28
The annual fun run, held along Auckland's waterfront, will not be going ahead.
In a Facebook post on Saturday night, the event organisers said they respected the alert level decision.
"We know how much all our participants were looking forward to [the] event day, but we respect the need to keep everyone safe and contain the spread of COVID-19."
Further details about whether it will be rescheduled are not yet known.
Weet-Bix Kids TRYathlon - Sunday, February 28
The event held in Christchurch's Jellie Park on Sunday has been cancelled as gatherings may not exceed over 100 people.
"The TRYathlon team is gutted but we completely understand the need to prioritise public health," organisers said.
"We will be running a TRY DIY - if you'd like to create your own TRYathlon experience at home, take some pictures and we'll make sure your kids can still get their medals."
Unfortunately, the organisers are unable to reschedule the event.
NZ Spirit Festival 2021 - March 4 to March 7
The NZ Spirit Festival to be held at the Tanglewood Retreat in Waimauku has been cancelled. The four-day event features the likes of Kiwi musician Tiki Taane, workshops, art installations and ceremonies.
It is not yet known whether the event will be rescheduled.
Outerfields - March 6
The Outerfields Festival at Auckland's Western Springs has been cancelled. The event was to be headlined by Benee, Fat Freddy's Drop, Montell2099 and other local artists.
Event organisers will provide an update on its Facebook page on Sunday.
