Severe turbulence during an Air Canada flight bound for Vancouver from Shanghai injured four flight attendants and forced the plane to make an emergency landing in Tokyo on Sunday night.

The trouble on Flight 38 arose about an hour into the flight, the airline said.

None of the 186 passengers on board the Boeing 767 were injured, Air Canada officials said. The flight attendants, who were all Canadian citizens, were taken to hospital, the airline said.

Air Canada spokeswoman Angela Mah said the four suffered mostly minor scratches and bruises, and three were released from hospital almost immediately after treatment. 

Officials were inspecting the aircraft and the passengers were to stay overnight in Tokyo

Severe turbulence rare

The Air Canada mishap occurred only hours after a Japanese domestic flight heading for Tokyo also ran into severe turbulence, injuring a cabin attendant and a passenger before landing safely at Haneda Airport as scheduled.

The JAL Flight 1348, carrying 373 passengers and 11 crew from Kobe, 435 kilometres west of Tokyo, hit unexpected turbulence just as it reached cruising altitude near Itami City, about 30 minutes into the flight, airline spokesman Kenji Okuyama said.

One passenger smashed against the over storage compartment and cut his forehead when he tried to stand up as the plane, a Boeing 777, hit turbulence and lost altitude, Okuyama said.

The flight had been smooth and the seatbelt signs were turned off until the sudden bout of turbulence, he said.

Mah said turbulence severe enough to cause injuries is rare and she couldn't recall a similar recent occurrence involving an Air Canada plane.

  With files from the Associated Press