Australia's Prime Minister says he's not putting a time limit on the search for the missing Malaysian airliner.

"We owe it to everyone to do whatever we reasonably can, and we can keep searching for quite some time to come, and we will keep searching for quite some time to come," he said.

As search crews headed out again to look for Flight 370, Prime Minister Tony Abbott said the intensity of the search and the magnitude of operations is increasing, not decreasing. At the same time he emphasized that this is a very difficult search.

"If this mystery is solvable we will solve it, but I don't want to underestimate just how difficult it is," said Abbot.

Some 20 ships and planes are involved in the search for debris from the missing jet.  It ended today with still no confirmation of debris and will resume tomorrow. The Malaysia Airlines Boeing 777 disappeared in the Indian Ocean more than three weeks ago with 239 people on board.