Auckland GP Peter Boot said it was common knowledge.
"Many people have proudly told me they have just rocked up to vaccination centres and been taken on, and not only them but usually their wives and families as well," Boot said.
Some people were travelling to clinics south of the city that were known to take walk-ins, he said.
"I think it's been very easy for people to get vaccines if they wanted to, by going to Māori and marae clinics and going out of town. Anyone who has seriously wanted one has been able to get one."
A Wellington woman who asked not to be named said it took her three weeks to secure a vaccine booking for her 87-year-old parents, who were only recently immunised.
Knowing others could walk-in without appointments was frustrating, she said.
"Word on the street they say just turn up at 4.30 in the afternoon, they'll have spare vials. I have heard anecdotally of people doing that and I've been advised to do that but it's not going to work for people who like following the rules and expect the system to work."
The health authority overseeing Auckland's 13 vaccination centres, the Northern Region Health Coordination Centre, could not say how many walk-ins or no-shows were happening.
"We are unable to provide this level of detail. But what we can say is that while we are following the Ministry of Health's vaccination framework we do take a pragmatic and flexible approach to meet the needs of our population," the centre said in a statement.
"In particular we take an equity approach to ensure that our Māori and Pacific populations are vaccinated, this includes their whānau and can include walk-ins at certain sites on a case by case basis."
It did not explain why some people who were not eligible were able to receive the vaccine earlier.
"On occasion if someone turns up at a community vaccination site without an invitation, if they are eligible, the sites take a pragmatic approach which means they consider how much supply they have and whether anyone has not arrived for their appointment and then determine whether the eligible person can be vaccinated that day or booked in for another day."
More than 11,500 people were being vaccinated a day in Auckland.
"All of our 13 community sites are very busy with bookings and we are not reliant on walk ins," the centre said.
"Our aim is to vaccinate as many people as possible as quickly as possible. There is enough vaccine for everyone in the country to be vaccinated by the end of the year."