ROV video frame grab from dive 13 showing metal box debris almost certainly from the shipwreck 700 m to the west. ATSB

The underwater search for Malaysia Airlines Flight MH370 found man-made objects on the ocean floor, later revealed to be debris from a nearby shipwreck. The Australian Transport Safety Bureau (ATSB), which is leading the search for the missing plane, said in its operational update Wednesday that sonar from Dong Hai Jiu 101 found the debris.

The man-made object turned out to be a metal box likely a part of an ancient shipwreck previously detected during the underwater search. Another site of interest inspected by the Remotely Operated Vehicle (ROV) on board the Chinese vessel Dong Hai Jiu 101 revealed only a rock formation.

"Dong Hai Jiu 101 has conducted a total of 13 ROV dives during the swing. Two dives were completed by Dong Hai Jiu 101 in the past week with one sonar contact identified as geology," ATSB said in the statement.

HH0009A Contact cluster on original sonar record. ATSB

Search authorities also said that Fugro Equator has been continuing its underwater search operations in the north of the 46,000 square-mile search area using the Autonomous Underwater Vehicle (AUV). So far, Fugro Equator has completed a total of 16 missions during the current trip.

"Three AUV missions were successfully completed this week, with an average duration of 27 hours," ATSB said.

Flight MH370 went missing on March 8, 2014, with 239 people on board while on its way from Kuala Lumpur to Beijing. A multimillion-dollar search for the missing plane has so far yielded no concrete clues as to the plane's whereabouts. The underwater search is expected to be completed by early 2017, following which the search will be suspended if no credible clues are found leading to the plane's fate.

"Ministers went to great lengths to explain this does not mean the termination of the search. Should credible new information emerge that can be used to identify the specific location of the aircraft, consideration will be given to determining next steps," ATSB said.