While most roads across the country have been nearly deserted, O'Sullivan says the number of people out and about in Kaitāia about midday was "ridiculous".
"Do I sound frustrated? Because I f***ing am," he said.
Northland District Commander Superintendent Tony Hill said police were aware of recent commentary and media reports that some members of the Northland community were failing to comply with the alert level 4 restrictions.
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Police had also received a number of complaints from the public reporting instances of people breaching the restrictions.
"It is critical that every single person complies with the alert level 4 restrictions and stays at home," Hill said.
"Those leaving their homes should only be doing so if they are essential workers or if you need to exercise or get essential supplies, such as groceries or medical items.
"The number of people out and about in the Kaitāia town centre over the past few days is unacceptable and disappointing."
Hill said it was clear that some people were leaving their homes for non-essential purposes and failing to follow the restrictions in place.
Some had been spoken to by police across Northland and additional staff had been deployed, he said.
"Our police officers will be engaging with the public, educating and encouraging people to comply with the restrictions.
"We don't want to be arresting people for not complying, however further enforcement action may be taken against those who are repeatedly refusing to comply with the restrictions."
Police would continue to monitor the situation closely, he said.
"We know the vast majority of Northlanders are doing the right thing and staying at home and we thank you for doing so," Hill said.
"As of this morning there are 11 confirmed cases of Covid-19 across Northland.
"It is everyone's responsibility to protect our whanau, neighbours and community and stay home, in order to minimise the risk of Covid-19 transmission and help keep everyone, and particularly our most vulnerable, safe."
A day after his viral video criticising the community's lax attitude to the lockdown, O'Sullivan praised the increased police presence.
"I know that the Kaitāia community will, and should be, grateful for your support now, as it has in the past.
While the increased number of officers was a sign of the seriousness of the lockdown, the issue of enforcing it was not unique to Kaitāia, he said.
"I think it also comes back to, how many people are actually hearing the message.
"There's certainly lots of people that are, and they're staying in their bubble, but what if you don't watch the news, what if you're not particularly interested in all of the press announcements that are going on ... that's probably a big issue here is that people aren't getting all of this information."
It was important that locals recognised the hard, and often unviable work of police while New Zealand is at alert level 4, O'Sullivan said.
