SYDNEY (Reuters/AFP) - An undersea search for missing Malaysia Airlines flight MH370 will be delayed by up to two months because of bad weather in the Indian Ocean during the southern winter, the authorities said on Wednesday (Oct 19).

The Boeing 777 disappeared on its way from Kuala Lumpur to Beijing in March 2014 with 239 passengers and crew on board, sparking a 2½-year search that has focused on the Indian Ocean.

The authorities from Malaysia, Australia and China initially expected to finish searching a 120,000 sq km target area by the end of 2016. "Due to poor weather conditions over the Southern hemisphere winter, it is expected searching the entire... area will be completed by around January/February 2017," they said in a statement.

Investigators will also deploy an underwater vehicle to take a closer look at objects found during a sonar survey of the southern Indian Ocean in the hunt for missing Malaysia Airlines MH370, Australia said on Wednesday.

Other so-called sonar contacts found in the investigation did not "exhibit the characteristics of a typical aircraft debris field" but some had "man-made properties" and needed to be eliminated as from MH370, the government agency leading the search, the Australian Transport Safety Bureau (ATSB), said in a statement.

"The ROV (remotely operated vehicle from Chinese ship Dong Hai Jiu 101) will be tasked to re-acquire and investigate, through video imaging, a range of sonar contacts which have been identified during previous deep tow operations," the ATSB said.

In what has been the most expensive search in aviation history, the authorities said they had searched 110,000 square km to date.

The search will be suspended once the target area is scoured, pending new information.

Why the aircraft went off course and came down are a mystery.

The only confirmed traces of the plane have been three pieces of debris found washed up on the island country Mauritius, the French island Reunion and an island off the coast of Tanzania.