President Barack Obama on Sunday offered continued US support for Malaysia in the search for missing flight MH370 but warned of a "laborious" task ahead to find the plane.

"It is a very challenging effort, a laborious effort and it is going to take some time," said Obama, who arrived in Malaysia on Saturday for a two-day stay.

The jet mysteriously disappeared on March 8 on a flight from Kuala Lumpur to Beijing with 239 people aboard and is thought to have crashed in the southern Indian Ocean.

But no trace has been found, leaving distraught relatives demanding answers and accusing Malaysia's government of a bungled response and possible cover-up.

Obama expressed the "deepest condolences of the American people to all the families who lost love ones on that flight".

"I completely understand the heartache the families are going through and want some answers. But I can tell you the United States is absolutely committed to providing whatever resources and assets that we can," he said during a joint press conference with Malaysian Prime Minister Najib Razak.

US experts were brought in shortly after the plane vanished to help with investigations.

American assets have been involved in a multi-nation search coordinated by Australia that has for weeks scoured the remote Indian Ocean for wreckage.

"I can say that the United States and other partners have found the Malaysian government eager for assistance and fully forthcoming with us in terms of the information that they have, and this is a joint effort," Obama added.

But he also made a point of urging transparency in investigations.

"I think it is very important ... that there should be full transparency in terms of what we know and what we don't know and how the process is proceeding," he said.

Najib expressed Malaysian gratitude for US help in the investigation and search.

Malaysia is the third stop on an Asian tour by Obama that has taken him to Japan and South Korea. He heads to the Philippines on Monday.