Grace Nathan, left, was among relatives of passengers of missing Malaysia Airlines flight MH370 who journeyed to Madagascar (AP)

A reward is being offered by relatives of those on the Malaysia Airlines plane that is believed to have crashed in the southern Indian Ocean to anyone who finds a piece of debris from the aircraft.

A group of relatives who travelled to Madagascar, off the south-east coast of Africa, made the offer in hope that residents will scour some coastal areas of the island, where possible parts of Flight MH370 washed ashore.

Meanwhile, a Malaysian official investigating the disappearance of the Boeing 777 was in Madagascar's capital, Antananarivo, to pick up debris that has already been found and will be analysed to see if it came from the aircraft.

"The more debris we find, the easier it will be to find where the crash happened," said Ghislain Wattrelos, a Frenchman who lost his wife and two of his three children when the plane deviated from its flight path from Malaysia to Beijing and vanished on March 8 2014.

Malaysia, Australia and China are close to completing a deep-sea sonar search, so far unsuccessful, of 46,000 square miles off Australia's south-west coast in the Indian Ocean.

They say they will suspend operations if there is no new evidence that could help pinpoint the crash site. Relatives of the missing believe the search should continue.

Mr Wattrelos, as well as two people who lost their mothers on the flight - Grace Nathan of Malaysia and Jiang Hui of China - spoke at a news conference in Antananarivo. They did not specify how much money might be given to someone who finds a confirmed piece of Flight MH370, saying it depends on the significance of the debris and the limited resources of the families.

"Everything is funded by us," said Mr Wattrelos, a business executive.

That includes the cost of flights, accommodation and other expenses that the relatives are spending on a week-long trip to Madagascar, which will include travel to coastal areas where plane debris may have washed up after drifting across the ocean.

There, they plan to hand out leaflets asking people to look for possible plane parts. Anyone who finds an item should note the time and place of discovery, take photographs and wrap the item in plastic and hand it to the nearest airport or police station, according to the leaflets.

The families say there are three major areas in Madagascar where Flight MH370 debris could have washed up: Isle Sainte-Marie, Antongil Bay and Nosy Be, a big tourist destination.

They also want people in Tanzania and Mozambique to be on the lookout. A piece found in Tanzania has been confirmed as part of the plane, while a couple of pieces found in Mozambique have been described as almost certainly coming from the plane.

Confirmation that the plane crashed came last year when a wing part washed ashore on Reunion Island in the western Indian Ocean, east of Madagascar.

AP