New Zealanders have become so keen to report their neighbours for breaking coronavirus lockdown rules that police on Monday said a website dedicated to addressing the issue crashed soon after going live.

The South Pacific nation is in the midst of a four-week COVID-19 lockdown, with residents under orders to stay at home or remain at least two metres (6.5 feet) apart if they must go outside.

Police commissioner Mike Bush said that a police website www.police.govt.nz/105support opened on Sunday afternoon and received such heavy traffic that it temporarily crashed.

"We've had 4,200 reports of people believing others weren't complying," he told reporters. "It shows how determined Kiwis are that everyone complies with us."

Bush said breaches included a party of about 60 people at a backpacker hostel in Queenstown and tourists continuing to travel the country in campervans.

Prime Minister Jacinda Ardern backed the informants and also urged the public to report any price gouging at supermarkets via a dedicated email address. "Now is not the time to bend the rules. This is a time to stay at home and save lives," she told reporters.

New Zealand, with a population of about five million, has 552 confirmed COVID-19 cases, one of them fatal.