PERTH, Australia, April 2 (Xinhua) -- About 10 planes and nine ships combed a broader swathe of sea in southern Indian Ocean on Wednesday but left searchers with no sign of the Malaysian MH370 jetliner more than three weeks after it vanished.
The 221,000-square-kilometer patch of sea, some 1,504 kilometers west northwest of Perth, doubled the size of the targeted area the previous day, according to the Australian Maritime Safety Authority (AMSA).
No sightings of any objects related to the missing flight have been reported although the weather in the search area was fair.
The AMSA has assembled a team of experts to model the movement of any debris of MH370 that might remain floating since March 8 when it mysteriously veered off course en route from Kuala Lumpur to Beijing with 239 people aboard.
The protracted international effort was boosted Wednesday with the join of British navy submarine, HMS Tireless, which has arrived in the area and is ready to contribute to locating the missing jet.
An Australian E-7A Wedgetail aircraft capable of deconflicting air space in the search area also assisted in the mission which has dragged on for more than three weeks but turned out to be fruitless as yet.
Hopes of a breakthrough had been raised after AMSA revealed a new search zone about 1,100 kilometers northeast of the previous one on Friday based on analysis that the plane had been traveling faster than previously thought.
Clock is ticking for finding black boxes of the jet as the battery-powered voice and data recorders could stop emitting " pings" about 30 days after the plane went missing. The Ocean Shield, an Australian warship with a black-box detector on board, is due to reach the search area on Thursday.
Ships and planes have focused on the Gulf of Thailand and South China Sea where the flight lost contact and then shifted west to the Strait of Malacca where it was last spotted by military radar. New analysis of satellite data then made experts believe that the jet had ended somewhere in the southern Indian Ocean.
Retired Air Chief Marshal Angus Houston, who heads the Joint Agency Coordination Center (JACC) coordinating the operation, said that limited flight data and hostile sea conditions made the hunt even more difficult.
"We don't have a precise aircraft location for six hours before the aircraft went into the water somewhere," he told the Australian Broadcasting Corporation on Wednesday.
The former defense force chief noted that the task to find the remains of MH370 will take time and if wreckage can not be found on the surface, they would eventually have to be "in consultation with everybody who has a stake in this, review what we do next."
At the invitation of Australian Prime Minister Tony Abbot, Malaysian Prime Minister Najib Razak is scheduled to arrive in Perth late Wednesday for a two-day official visit.
Najib will tour Royal Australian Air Force Base Pearce on Thursday to personally thank the international forces involved in the MH370 hunt and receive briefings from the newly formed JACC.