(Recasts paragraph 1 with airline statement, passenger comments in paragraphs 5 and 7, updates share movement in paragraph 11; changes keywords for media clients)

March 11 (Reuters) - At least 50 people were hurt when a Boeing 787 operated by LATAM Airlines dropped abruptly mid-flight from Sydney to Auckland on Monday, according to the airline and a New Zealand health service organisation that treated the injured.

The aircraft landed at Auckland airport as scheduled on Monday afternoon, according to FlightAware.

"LATAM Airlines Group reports that flight LA800, operating the Sydney-Auckland route today, had a technical event during the flight which caused a strong movement," the carrier said.

One person is in a serious condition while the rest suffered mild-to-moderate injuries, a spokesperson for Hato Hone St John, which treated roughly 50 people at the airport, said. "The plane, unannounced, just dropped. I mean it dropped unlike anything I've ever experienced on any kind of minor turbulence, and people were thrown out of their seats, hit the top of the roof of the plane, throwing down the aisles," passenger Brian Jokat told the BBC.

The cause of the apparent sudden change of trajectory could not be ascertained immediately. Safety experts say most airplane accidents are caused by a cocktail of factors that need to be thoroughly investigated.

"Some of the roof panels were broken from people being thrown up and knocking through the plastic roof panels in the aisle ways. And there was blood coming from several people's heads." Jokat, who was not injured in the incident, said.

He said passengers who were doctors on the plane provided bandages and neck braces for people who were severely injured.

The eight-year-old Boeing 787-9 Dreamliner, according to flight tracking website FlightRadar24, was on its way to Santiago via Auckland.

In 2008, dozens of people were injured when another wide-body jet, an Airbus 330 operated by Qantas Airways, dropped sharply because of faulty readings from a flight data computer while heading for Perth in Australia.

Boeing said it was working to gather more information and will provide any support to the airline. Its shares were down 3% in U.S. morning trading.

The Wall Street Journal reported on Saturday the U.S. Department of Justice has opened a criminal investigation into 737 MAX mid-air cabin-panel blowout on an Alaska Airlines flight in January. (Reporting by Urvi Dugar, Shivansh Tiwary, Gursimran Kaur, Abhijith Ganapavaram in Bengaluru, Tim Hepher in Paris and Lewis Jackson in Sydney; Editing by Jamie Freed and Arun Koyyur)