A privately funded search for missing Malaysia Airlines flight MH370 has ended.

US-based company Ocean Infinity had been using a deep-sea vessel to conduct a 90-day survey of a vast area of the southern Indian Ocean.

A message board at Kuala Lumpur airport shortly after the plane disappeared - the reason why remains a mystery -- Photo: REUTERS

But it found nothing and Malaysia's government says it has no plans to begin any new searches.

The plane disappeared on 8 March 2014 while flying from Kuala Lumpur to Beijing with 239 people on board.

There are still fierce debates over how the flight ended and many of the families of those on board say they want search efforts to continue.

Grace Nathan, whose mother was on MH370, said she was opposed to ending the search.

"People might think: 'Why are these people still harping on about this, it's been four years'. It's important for people to remember that MH370 is not history," she told the Guardian newspaper.

The plane was carry 153 people from China and 38 Malaysians. Other passengers came from Iran, the US, Canada, Indonesia, Australia, India, France, New Zealand, Ukraine, Russia, Taiwan and the Netherlands. The 12 crew were all Malaysian.

Ocean Infinity surveyed an area of about 80,000 sq km (30,888 sq miles), using a fleet of up to eight mini-submarines.

The deteriorating weather in the area as winter approaches now makes operating there impossible for the next few months.

The company had agreed to undertake the search unpaid but would have received a reward of up to $70m if it had found the wreckage.

How did the flight end?

Investigators have very limited information about the plane's last hours.

Experts still cannot come to a definitive conclusion as to whether MH370 remained under the pilot's command, or crashed out of control into the sea.

Each of these two scenarios suggests different search areas.

The reasons why the pilot took the airliner off its scheduled flight path and down into a remote stretch of ocean are still unknown, as most of the communication equipment on board had been switched off.

Earlier this month, Australian investigators rejected suggestions that the plane was deliberately brought down by the pilot.

How the mystery unfolded

8 March 2014: Malaysia Airlines flight MH370 departs for Beijing. The plane loses contact less than an hour after take-off, with no distress signal or message sent. Initial search efforts focus on the South China Sea

15 March 2015: After evidence emerges that the plane was diverted to the south, the focus switches to the Indian Ocean

July 2015: Large piece of debris washes ashore on Reunion, an island in the Indian Ocean east of Madagascar

January 2017: The governments of Australia, Malaysia and China announce they are suspending the official search after failing to find anything in the area thought to be the plane's final resting place

January 2018: Amid pressure from relatives, Malaysia signs a deal with a private company to resume the hunt

May 2018: The latest search ends, with Malaysia saying it has no plans to restart it.

Source: BBC