An American Airlines Boeing 777-200, registration N766AN performing flight AA-170 from Tokyo Narita (Japan) to Los Angeles,CA (USA) with 231 people on board, was climbing through FL240 about 194nm east of Narita Airport over the international waters of the Pacific Ocean when the aircraft experienced severe turbulence causing injuries to 4 flight attendants. The crew continued the flight to Los Angeles where the aircraft landed safely about 9 hours later.
The NTSB reported on Apr 20th that two flight attendants located in/near the aft galley at the time of the turbulence received serious injuries, two other flight attendants received minor injuries. The airplane received no damage. A representative of American Airlines told the NTSB that the airplane was climbing through FL240 when the aircraft experienced about 10-15 seconds of severe turbulence.
https://flightaware.com/live/flight/AAL170/history/20110411/0625Z/RJAA/KLAX
via Accident: American B772 near Tokyo on Apr 11th 2011, turbulence injures 4 cabin crew.