By Alasdair Pal and Cordelia Hsu

SYDNEY (Reuters) -New Zealand's Transport Accident Investigation Commission said on Tuesday it was seizing the cockpit voice recorder and flight data recorder of a LATAM Airlines (OTC:) Boeing (NYSE:) 787 after an incident that left more than 50 people injured.

The airline and passengers aboard the Sydney-Auckland flight on Monday said the plane with 263 passengers and nine crew members on board dropped abruptly mid-air.

"My neighbour who was in the seat two over from me, there was a gap in between us, as soon as I woke I looked and he was on the ceiling and I thought I was dreaming," Brian Adam Jokat, a Canadian citizen residing in the UK who was travelling on the plane, said on Tuesday.

Photos taken by Jokat after the incident showed damage sustained to the ceiling of the airplane where he said fellow passengers had hit it.

The New Zealand accident investigator said Chilean authorities had confirmed they had opened a probe into the flight, and it was assisting with their enquiries.

A spokesperson for TAIC said because the incident occurred in international airspace it fell to Chilean accident investigation authority Direccion General de Aeronautica Civil (DGAC) to open an inquiry.

LATAM is based in Chile and the flight was due to continue on to Santiago after stopping in Auckland.

"TAIC is in the process of gathering evidence relevant to the inquiry, including seizing the cockpit voice and flight data recorders," the New Zealand agency said, referring to the so-called "black boxes" that will provide more information on the flight's trajectory and communications between pilots.

DGAC said in a statement it was working with TAIC on the investigation.

LATAM did not immediately respond to a request for comment on whether it had given the black boxes to TAIC. The airline said earlier on Tuesday it would assist the relevant authorities on any investigation into the "strong shake" during the flight.

The cause of the apparent sudden change in trajectory of the flight is currently unexplained. Safety experts say most airplane accidents are caused by a cocktail of factors that need to be thoroughly investigated.

New Zealand's Civil Aviation Authority said in a statement it would also assist in the investigation if required.

There has been renewed debate over the length of cockpit recordings in the aviation industry since it was revealed voice recorder data on the Alaska Airlines Boeing 737 MAX 9 jet that lost a panel mid-flight in January was overwritten.