Malaysian authorities have confirmed that a new hunt for flight MH370 is expected to end by mid-June.
The Malaysia Airlines jet disappeared on 8 March 2014 while en route from Kuala Lumpur to Beijing with 239 people, mostly from China, on board.
No sign of the plane was found in a 120,000 square sea search zone and the Australian-led hunt, which was the largest in aviation history, was suspended in January last year.
But the Malaysian government struck a "no find, no fee" deal with exploration firm Ocean Infinity to resume the search in an area north of the original zone, that scientists now believe is the likeliest crash site.
The hunt restarted in January, with a research vessel deploying eight high-tech drones to scour the seabed.
Officials had said the search would last a maximum of 90 days.
Speaking as families of the disappeared marked four years since the plane vanished in the Malaysian capital, the country's civil aviation chief Azharuddin Abdul Rahman said that this would be spread over several months as the ship needed to stop sometimes to refuel.
The hunt is expected to end by mid-June, he said.
"Hopefully, we will be able to identify the location of MH370," he said at the anniversary event at a Kuala Lumpur shopping mall.
By the end of February, research vessel Seabed Constructor had surveyed 8,200 square kilometres of the 25,000 square kilometre search area, according to Ocean Infinity's most recent update.
At Saturday's event, relatives of the missing passengers spoke of their continuing sense of pain and loss.
But the new search meant there was also a glimmer of hope.
Jacquita Gonzales, whose husband Patrick Gomes was a steward on the flight, told the event she was grateful that the Malaysian government they had restarted the search.
"They have not given up hope, and neither have we."
K. S. Narendran, whose wife Chandrika Sharma was on the flight, was more cautious.
"Am I hopeful? It's hard to say -- there are a number of 'ifs'," he told AFP. "If the data is right, if the analysis is right, if they are searching in the right area."