Twenty-five Bangladeshi men who tried to enter the country without a visa are likely victims of people smugglers, Immigration New Zealand (INZ) says.
It was worried by the size of the group and said it was extremely unusual.
The men had electronic travel authorities, or ETAs, for a stopover in New Zealand but were denied boarding in Dhaka.
Inquiries suggested they were not going to transit to Australia or to take a cruise, as they could with an ETA, and instead intended to stay in New Zealand.
"The way that the immigration systems work is we check the information of the passenger and check against immigration records and other records.
"And we were able to say very quickly those passengers did not have a visa to enter Australia, they did not have to travel booking to take them to Australia. It quickly became evident that they were attempting to board that flight inappropriately."
INZ national border manager Peter Elms said it highlighted the people smugglers, who exploited people's dreams of coming here.
He suspected they had been fooled and paid a lot of money before being found out.
"I think it's quite possible that there is a facilitator in the background, who is advising people that they can obtain travel authorities or visas for people to come to New Zealand.
"We are seeing an increase in the number of people who have attempted to travel illegally, and on average INZ prevents about 400 people every month from being able to board planes to come here."
The large group coming from Dhaka was extremely unusual, he said, but demonstrated the lengths people would go to to reach New Zealand.
"It also shines a light on the people smugglers who work behind the scenes to try and find gaps in border security systems worldwide, and their willingness to exploit vulnerable migrants. Because at the end of the day, all they're worried about is the money.
"So this is a message that goes out to those would-be smugglers that New Zealand is alert to that and that their attempt to do this will not go undetected. And that we will look into the background, the circumstances of these cases and where we do find evidence to indicate who the perpetrators are, we will take action."