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Since it was announced at 1pm, the service has been used extensively.
Police have warned police to be patient due to "very heavy traffic".
"People reporting suspected breaches of alert level 4 restrictions via online reporting on the police website are asked to be patient," police said in a statement.
"If you are having difficulty, please try again later."
Prime Minister Jacinda Ardern announced the nationwide lockdown on Monday in response to the ongoing spread of Covid-19.
The lockdown is in place for four weeks at least and means everyone must stay home and self-isolate - apart from people considered part of the "essential services central workforce".
Authorities including police have the power to stop people out and about and question them about why they are not at their home.
If necessary people can be arrested and charged.
It is understood just one person is before the courts at this stage as a result of breaching the national lockdown.
Today the new reporting service went live.
Police said it can be used to report isolation breaches or cases of businesses continuing to operate when they are not part of the essential workforce.
Commissioner Mike Bush urged people to use the online form instead of calling police.
The New Zealand Herald has learned that the 105 non emergency number had been inundated this week and was under immense pressure.
The online reporting service should ease that.
"We know that people want to do the right thing if they see people flouting the restrictions, but we want to ease the load on the non-emergency phone number," said Bush.
"Police will take the information reported online and make contact to remind those breaching the restrictions of their responsibilities.
"We are continuing to take the approach of educating and informing people of their responsibilities in the first instance, but we will not hesitate to take enforcement action if people continue to ignore the restrictions."
Prime Minister Jacinda Ardern said she was "frustrated" by reports of people not following the lockdown rules.
So far, some 2000 calls have been made about people breaching the lockdown restrictions.
Bush said police did not want to have to make arrests or chase people up for "doing the wrong thing".
"Please stay at home, follow the guidelines on www.covid19.govt.nz and don't give people a reason to report your behaviour to police," he said.
Police said this afternoon that once going live at 1pm today, the new form has experienced very heavy traffic.
"If you are having difficulty, please try again later," they said.
Four days into the national lockdown Kiwis are still confused about the rules and how strict the "stay at home " message is.