SYDNEY (Reuters) - Adverse weather has caused a delay of up to eight weeks in the Indian Ocean search for missing Malaysia Airlines flight MH370, search officials said on Wednesday, pushing the hunt well beyond an expected conclusion date of mid-2016.

The jet carrying 239 passengers and crew disappeared enroute from Kuala Lumpur to Beijing on March 8, 2014, in one of aviation's great mysteries. A wing part, known as a flaperon, washed up on the French island of Reunion in July 2015.

Crash investigators have otherwise confirmed no other trace of the plane. An undersea search of the southern Indian Ocean, history's costliest such effort, has turned up nothing.

"Poor weather conditions have severely impacted search operations," the Joint Agency Coordination Centre in charge of the search said in a statement.

"Progress has slowed, with only a minimal area searched" since the start of the southern hemisphere winter, it added.

The search has covered 110,000 sq km (42,000 sq miles) of ocean floor, leaving just 10,000 sq km (3,800 sq miles) unchecked, said the agency, which represents the Australian, Malaysian and Chinese authorities spearheading the effort.

The poor weather will permit some use of deep tow equipment, but an autonomous underwater vehicle that surveys the most difficult stretches can only be launched in the calmer conditions of spring and summer, the agency added.

If the weather remains hostile or equipment fails, the search "may continue well beyond the winter months," it said.

The agency had originally expected to wrap up its search of about 120,000 sq km (46,000 sq miles) of ocean floor in mid-2016.

(This story has been refiled to fix spelling of "investigators" in paragraph 3)

(Reporting by Byron Kaye; Editing by Clarence Fernandez)