By Robb M. Stewart and Ross Kelly 

MELBOURNE, Australia--The hunt for Malaysia Airlines Flight 370 continued Monday with a U.K. military vessel en route to check out signals detected by a Chinese ship over the weekend, as locator beacons attached to the plane's "black box" flight recorders near the likely end of their battery life.

Locator beacons on two flight recorders aboard the plane have an estimated battery life of about 30 days before they stop emitting signals. Monday marks the 30th day since the Boeing 777 200 jetliner vanished from civilian radar on a flight from Kuala Lumpur to Beijing on March 8 with 239 people on board. The devices, if found, could provide vital clues to what occurred on the ill-fated flight.

Nine military and three civilian aircraft were set to join 14 ships scouring a stretch of roughly 234,000 square kilometers (90,000 square miles) in the southern Indian Ocean for the black boxes and debris from the jetliner, Australia's Joint Agency Coordination Centre, which is coordinating the multinational search, said Monday.

Good weather was expected throughout the day, with rain showers forecast for the afternoon unlikely to affect the search, the agency said.

The U.K. Royal Navy ship HMS Echo is on its way to assist the Chinese vessel Haixun 01, which reported detecting several "acoustic pings" on Friday and Saturday about 2 kilometers (1.2 miles) apart. The signals were thought to be consistent with frequencies belonging to the missing aircraft's flight recorders.

An Australian naval ship, Ocean Shield, picked up separate pulse signals on Sunday about 300 nautical miles away and was continuing to search that area, the Joint Agency Coordination Centre said Monday. The Australian vessel has been fitted with U.S. Navy black-box detector equipment that is able to detect signals from the flight recorders at deeper levels than the Chinese device. The Chinese listening device was designed to identify sounds at depths of less than 1,000 feet, according to one person briefed on the Flight 370 probe, while the ocean bottom in parts of the search area exceeds 13,000 feet.

It is still far from certain the pings are from the missing plane. Air-safety experts say other maritime locating devices also use similar frequencies. Following a signal that search teams detected on April 3 but later discounted, the Australian agency warned that biological sources, such as whales, and shipping could lead to false alerts. Further complicating the search, the pulse signals received were patchy.

Nevertheless, retired Air Chief Marshal Angus Houston, who is in charge of the Australian search agency, has said the Chinese findings were an important and encouraging lead.

The search area where Flight 370 is thought to have hit the ocean continues to be refined based on technical analysis by air crash investigators from Malaysia, the U.S., the U.K., China and Australia. Authorities are now focusing on the southern part of the designated search zone, which has been divided into three dispersed blocks, based on the latest analysis that suggests the missing flight traveled slightly farther south than previously thought.

"The area of highest probability we think is now probably in the southern part of the area pretty close to where Haixun 01 is operating," Air Chief Marshal Houston said Sunday. When it detected the pings, Haixun 01 had been searching in an area of the southern Indian Ocean close to but still outside three designated search zones. Air Marshal Houston dismissed the idea that China was acting unilaterally.

"China's sharing everything that's relevant to this search," he said, adding that the agency was "very satisfied" with the "consultation and coordination" it was receiving from China, which lost 153 citizens aboard the missing plane.

The focus of the search for Flight 370 swung abruptly to the southern Indian Ocean on March 20, based on satellite images of possible plane debris. It later shifted around 700 miles to the north of the first search zone in the ocean after further calculations were made to radar data.

Now in its fifth week, the hunt for Flight 370 so far has yielded only unrelated scraps of junk. Last week, the search was joined by a U.K. military submarine equipped to detect signals from the flight-data and cockpit voice recorders. The nuclear-powered HMS Tireless, built for the Royal Navy as a Cold War attack vehicle, has equipment on board that may also help pinpoint signals from Flight 370's recorders. It could also be used to search for aircraft wreckage along the largely undisturbed seabed.

Andy Pasztor contributed to this article.

Write to Robb M. Stewart at robb.stewart@wsj.com and Ross Kelly at ross.kelly@wsj.com

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