The Americans send a special undersea drone to help search for MH 370 in deep waters.

 Reuters reports the United States is sending an undersea Navy drone capable of exploring waters nearly 15,000 feet deep to potentially help search for any sunken wreckage.

The Pentagon announced the US is pre-positioning the sonar-equipped Bluefin "autonomous underwater vehicle" in Australia to help pinpoint the plane.

The Bluefin drone is just over 17 feet (5 meters) long and weighs 1,764 pounds (800 kg), according to a Navy factsheet. Kirby said it can operate for more than a day at slower speeds.

The undersea Navy drone was flown out of a New York airport on Monday and were expected to arrive in Perth, Australia on Tuesday, the Pentagon said.

Ten American civilian personnel and uniformed members of the military were also flying to Australia to operate or prepare the equipment, it said.

But the Pentagon cautioned that the US technology would only be employed once the search area was significantly narrowed.

"In order for this technology to be useful, you have to have an identified area on the sea bottom that you want to go take a look at," Mr Kirby said.