An Air New Zealand plane window that started cracking mid-flight forced the pilot to drop altitude suddenly today, leaving at least one passenger fearing for his life.

The 2pm flight 8835 from Hokitika to Christchurch suddenly dropped altitude while flying over the Southern Alps, passenger Haydn Draper told 1 News.

Draper said water cups flew up to the ceiling as the plane dropped.

"I don't mind a bit of turbulence on a plane, it can be fun, but I thought I was going to die," he told 1 News.


Passengers then saw the plane's windscreen was cracked when they were on the tarmac, but those who filmed or took photos were stopped by staff and told to delete them, 1 News reported.

Draper managed to keep his footage, which clearly shows big cracks in one windscreen pane.

An Air NZ spokesperson told 1 News when the cracking developed the pilot had followed protocol and dropped altitude.

Passengers had been asked to delete their footage because of restrictions around using mobile phones on the tarmac.

Aircraft windscreens are made of separate panes of glass, and cracking in one layer "in no way risked the integrity of the windscreen", the spokesperson said.

The Herald has contacted Air NZ for comment.