An Air Nelson passenger booked on what she thought was a direct flight from Rotorua to Wellington this morning says the airline picked up "hitchhikers" in Palmerston North en route.

The passenger is a regular on the Monday, 6:45am, Air Nelson direct flight from Rotorua to Wellington. Air Nelson is an Air New Zealand subsidiary.

Speaking on condition of anonymity, the woman passenger said she was told the Wellington-bound flight would be diverted to Palmerston North to pick up passengers when she checked in at Rotorua Airport this morning.

"I'm a regular on the direct flight. That's why I purchase my ticket on the flight because we get in to Wellington to start work about 10 to eight every Monday morning," she said.

The flight arrived in Wellington about 40 minutes late at 8:30am, she said.

"If I'd known we were going to pick up hitchhikers in Palmerston North I would have made alternative arrangements," the woman said.

There were about 40 people on the flight.

"We were on the ground there for about 20 to 25 minutes. I just wish we'd been told this was going to happen before we booked our direct flight tickets," the woman said.

An Air New Zealand spokeswoman said the flight was briefly diverted to Palmerston North to collect 15 passengers who were unable to travel due to the cancellation of a Palmerston North to Wellington flight.

An engineering fault had affected their plane, she said.

"The Rotorua-Wellington service arrived into Wellington at 8.30am - around 40 minutes later than scheduled. We apologise for any inconvenience to passengers. However this enabled other customers to avoid a far more lengthy delay," the spokeswoman said.