The woman flagged down a local officer who was driving past at the time of the incident.
The off-duty officer spoke to people about the incident before calling for another police unit to attend, the spokesman told the Herald.
The woman said the off-duty officer blocked the boat ramp, however, the spokesman denied that was the case.
"The occupants of the dinghy left the immediate area before the on-duty officers arrived and currently remain out on the water," the spokesman said around 5pm.
The fishermen headed out towards the harbour where the woman suspected they were heading to Eastern Beach or Howick Beach around the corner.
"They've now left the estuary and the second police car has just arrived,' the woman told the Herald about 2.30pm.
"We suspect they'll be going to Eastern Beach or Howick Beach or somewhere like that to try and retrieve the boat.
"I would suspect they would be very local because anyone towing a boat, it would be really suspicious."
The fishermen were not the first law-breakers the woman saw, another boat with an adult and child flew down the estuary sometime before.
Fisheries New Zealand had been notified about the incident and police were still monitoring the matter, the police spokesman said.
Director-General of Health Dr Ashley Bloomfield announced the new laws in a health notice to help the country move out of lockdown as soon as possible.
"We want people to stay safe, but if a small number of people persist in deliberately flouting the restrictions, police will have the discretion to warn or, if necessary, to arrest.
"Outside of that, we are asking people to stay local, apply common sense and not do anything that could risk exposure to injury or require search and rescue services."