A massive hunt for the missing Malaysia Airlines plane resumed on the 28th day on Saturday with newly mobilised underwater search effort, China's Xinhua news agency reported.
Up to 10 military planes, three civil jets and 11 ships will join the search for flight MH370, including Australian navy vessel Ocean Shield and British oceanographic vessel HMS Echo tasked with underwater operations.
An area of about 217,000 square kilometres, 1,700 kilometres northwest of Perth will be scanned with the aid of fair weather conditions, the Australian Maritime Safety Authority (AMSA) said.
Ocean Shield equipped with a U.S. towed pinger locator and HMS Echo will continue scouring a single 240 kilometre underwater track converging on each other.
The sub-surface search was launched on Friday in an attempt to recover the plane's black box that contains a pinger with a battery life of 30 days after a crash.
The towed pinger locator is capable of picking up emissions from the black box pinger up to 6,100 metres under sea surface while the Echo is fitted with an array of sensors and sidescan sonar for surveying the ocean floor.
MH370 with 239 people on board is believed to have crashed on March 8 in the southern Indian Ocean west of Perth, although no confirmed debris has been found from the plane.
"The underwater scan zone has been chosen based on analysis by the investigative team from five nations of the most likely aircraft track to where the aircraft might enter into the water," said Angus Houston, chief of Joint Agency Coordination Center (JACC) who leads the search.
Houstan said the visual search will go on as it may find wreckage on the surface that would result in the further narrowing down of the search area.