Jetstar was forced to offload 22 passengers just before take-off for the Cook Islands to load more fuel because of threatening weather at alternate airports.

One passenger said it was an ''appalling failure'' by the airline last night whose staff read a list of passengers who wouldn't be able to board the plane.

He said those ''unlucky souls'' were told the plane about to depart from Auckland was overloaded but they could have a flight tomorrow.

The disruption caused angst for passengers as they had to re-enter customs and then hang around while confused workers attempted to make arrangements, said the passenger from flight JQ129.

''To disrupt so many passengers at the boarding gate shows a level of incompetence rarely seen in the contemporary airline industry.''

But a Jetstar spokesman said the offloaded passengers were offered accommodation where required and provided a $200 flight voucher.

''Due to forecast weather conditions we needed to reduce the weight on our flight from Auckland to Rarotonga on Thursday evening in order to take extra fuel,'' he said.

This was needed because of forecast fog in Auckland and bad weather in Tahiti - alternate landing ports if the aircraft was prevented from landing in the Cook Islands for any reason.

''We appreciate that weather-related disruptions are inconvenient for our passengers and thank them for their patience, however we always put safety before schedule.''

Due to forecast poor weather conditions, airlines need to carry additional fuel on some routes. This may mean baggage, and sometimes passengers, need to be offloaded from a flight to manage weight requirements.

The flight on an Airbus A320 took off 25 minutes late and the flight time was about 45 minutes more than the one on the day before.

If they have to offload passengers airlines will call for volunteers, take into account any special personal circumstances and may give priority to those who had checked in early.