HONG KONG (AFP) - A dozen people were injured when a Cathay Pacific jumbo jet hit "rollercoaster" turbulence over northern Japan, local media reported on Wednesday.

The Boeing 747-400, carrying 321 passengers and 21 crew, was rocked by "sudden turbulence" when it flew over Hokkaido prefecture on Tuesday, the South China Morning Post reported.

Cathay Pacific confirmed to AFP that two crew members were injured along with a number of passengers, without confirming the newspaper's figure.

The flight from San Francisco to Hong Kong landed at the southern Chinese city's airport at 6.26pm local time to be greeted by a fleet of ambulances and emergency vehicles.

One of the injured was taken to hospital on a stretcher.

The turbulence was "more intense than riding a rollercoaster", a passenger was quoted by the newspaper as saying.

The airline said medical assistance was provided to the injured on board before the flight landed.

"Hong Kong Civil Aviation Department has been informed of the incident, and we are collaborating with the authority on the investigation," the spokesman said.

Cathay Pacific is Hong Kong's flagship airline.