An Air NZ flight from Houston to Auckland had to be diverted because of a medical emergency.

An Air New Zealand flight from Houston to Auckland has been thrown way off schedule after a medical emergency on board.

According to a tweet from Raewyn Rasch - a passenger onboard flight NZ29 - fuel was dumped before landing in Los Angeles for the emergency.

The pilot had told passengers a young man had fallen ill, she said.

Flightradar24.com shows how the flight changed course.

In a statement, an Air New Zealand spokeswoman said the flight was diverted to Los Angeles because of a medical emergency on board.

"The passenger concerned has remained in Los Angeles for medical treatment and the flight has since departed," she said.

Due to the additional flight time, the aircraft would stop briefly in Nadi where it would change pilots and cabin crew before continuing to Auckland.

Another person who said they were onboard, Sam Barley, said every one was dealing with the situation well.