Four people, including three crew, have been injured after an Air New Zealand flight hit turbulence, 40 minutes into a Vietnam-Auckland flight.

Passengers have described the experience as a "flight from hell".

One passenger on the plane said it dropped 100ft.

"It came on so fast. 20 seconds of bumps then a drop off then five seconds later up we went followed by a 100-foot fall," said passenger Vince Newbold.

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Another passenger said crew were thrown to the ceiling.

She posted on Facebook the plane was first delayed by two hours because of an issue with the brakes.

Then the "flight from hell" took off with everything going well until the plane struck turbulence an hour into the flight.

"As the air hostess hands me my tray we hit some really bad turbulence, the plane drops and all my food flies all over the floor and me.

"Everyone is screaming and we have no idea what is going on.

"A few minutes pass and the crew calling for a doctor over the loud speaker, two crew members had suffered critical injuries, the turbulence had thrown them up to the ceiling, another was injured."

She said she was back in Vietnam because the plane returned to Ho Chi Minh City to get them to the nearest hospital.

She posted that as well as losing all food trays, four carts were left smashed over the floor.

Paramedics boarded the plane to tend to the injured once the plane landed back in Vietnam.

She posted the frightening episode in the skies was unlike anything she had ever experienced.

Newbold said as the plane hit turbulence, "things went flying".

"Two cabin crew are injured with head injuries and a doctor on board said we need to land ASAP," he wrote in an email.

A decision was made to return to Vietnam as Darwin was deemed too far away for urgent treatment.

Newbold described it as "spooky" and better than any roller coaster he had even been on.

The four people onboard flight NZ268 from Ho Chi Minh City all suffered minor injuries in the incident yesterday morning, an Air New Zealand spokeswoman said.

The aircraft landed safely and without further incident in Vietnam around 8.20am Sunday New Zealand time.

The injured were assessed and treated by medical staff.

The flight returned to Vietnam and departed again this morning. It is due to arrive in Auckland this evening.

"We thank customers for their patience," the spokeswoman said.