Families of passengers aboard missing Malaysia Airlines flight MH370 said on Saturday they still had hope that the plane will be found, as they marked the fourth anniversary of one of the world's greatest aviation mysteries.

Flight MH370, carrying 239 people, went missing on its way from Kuala Lumpur to Beijing on March 8, 2014.

Australia, China and Malaysia ended a fruitless A$200-million ($159.38 million) search of a 120,000 square-kilometre area in January 2017, despite investigators urging that the search be extended 25,000 sq km further north.

A year later, Malaysia agreed to pay U.S. firm Ocean Infinity up to $70 million if it finds the plane within 90 days. The search vessel, the Seabed Constructor, began its search on Jan. 23.

Investigators believe someone may have deliberately switched off MH370's transponder before diverting it over the Indian Ocean.

Debris has been collected from Indian Ocean islands and Africa's east coast and at least three pieces have been confirmed as coming from the missing plane.