An Air Canada flight has made an emergency landing in Honolulu after 37 passengers on board were injured after the plane encountered turbulence near Hawaii.

Flight AC33, carrying 269 passengers and 15 crew, was flying from Vancouver to Sydney when the Boeing 777 aircraft “encountered unforecasted and sudden turbulence approximately two hours past Hawaii”, the carrier said on Thursday.

The plane was diverted to Honolulu and landed safely at 12.45pm on Thursday (1.45am AEST Friday) after hitting turbulence at 10,900 metres, almost 1000 kilometres southwest of Honolulu.

“As a precaution, medical personnel are on standby to examine passengers in Honolulu,” the carrier said.

The Associated Press reported nine passengers were seriously injured, with almost 30 taken to nearby hospitals in Honolulu, describing a “bloody” scene inside the main cabin.

Llyn Williams was traveling with his wife Erica Daly back to their home in Sydney.

Mr Williams said the scene was frightening, with “a lot of blood everywhere” as almost all passengers not wearing seatbelts hit the ceiling.

Honolulu Emergency Medical Services Chief Dean Nakano says the injured ranged from children to the elderly.

The Air Canada flight was almost six hours into its journey before it suddenly decelerated, causing oxygen masks to fall, forcing sleeping passengers to hit the ceiling.

“We hit turbulence and we all hit the roof and everything fell down, and stuff … people went flying,” passenger Jess Smith, from Newcastle, told CBC News.

“I watched a whole bunch of people hit the ceiling of the plane,” said another passenger Alex MacDonald.

“A couple of the air hostesses were bringing food out at the time, and they hit the roof as well. But as a whole people seem to be OK; didn’t seem to be any major injuries.”

She told the ABC “everyone hit the ceiling of the plane”: “I was asleep and I started to wake up from the plane rocking”.

“As I sort of woke up the plane dropped out of nowhere and I was plunged from the seat, hitting the roof.

“A girl in front was bleeding,” she said.

The ABC reported Ms Smith’s partner, Tay Maggs, received a bloody nose after being launched from her seat.

“My nose is sore and bruised … now I know why you should always wear the seatbelt”.

Hurricane Fall, a band from Newcastle, were also on the flight, with their vocalist Pepper Deroy injuring his forearm and elbow.

“It started getting a little bit rocky so I thought I better buckle up and then about five seconds later, you just watched everyone head in the plane who wasn’t wearing a seatbelt – just hit the roof like a jack-in-the box,” band member Tim Trickey told the ABC.

Passenger Luke Wheeldon told Honolulu news station KTIV about half the passengers weren’t wearing seatbelts: “There was no warning and then half of them, their head hit the roof all at once,” he said.

“And I went, ‘Oh, this is a bad day.”‘

-with agencies