The search for missing Malaysia Airlines flight MH370 off Western Australia could take years, a senior US Navy official said, as search and rescue officials raced to locate the plane's black box recorder days before its batteries are due to die.
Ten ships and as many aircraft are searching a huge area in the Indian Ocean west of Perth trying to find some trace of the aircraft, which went missing more than three weeks ago and is presumed to have crashed.
The Malaysian Government announced moves to tighten airport security, but the head of the US senate intelligence committee said there was no evidence that terrorism had any role to play in the flight's disappearance. "There's speculation, but there's nothing," said Senator Dianne Feinstein. "This is a very difficult mission."
Among the vessels to join the search is an Australian defence force ship, the Ocean Shield, that has been fitted with a sophisticated US black box locator and an underwater drone.
Captain Mark Matthews, a US navy officer who is in charge of the black box pinger detector, said the search area needs to be significantly reduced before there is any serious prospect of finding the black box.
"Right now the search area is basically the size of the Indian Ocean, which would take an untenable amount of time to search," he said.
Dr Todd Curtis, an aviation expert and former Boeing engineer, warned that the hunt for the plane could last for years. He said the black box was unlikely to be found before its 30-day pinger, which helps searchers to locate both the box and the plane, runs out of battery life in about a week.
"The likelihood of finding the plane quickly, especially given the pinger will soon end, is going down astronomically," he said.
Watch: MH370: Families still seek answers
"Even if they found the debris today, there is the problem of estimating where it drifted over the past three weeks and then estimating the new area. It all has the potential to take much more than two years."
Curtis said the search was likely to be very prolonged and may end in failure. "There is a chance they will never find the plane," he said.