An Australian navy vessel searching for a missing Malaysian airliner has picked up deep-sea acoustic signals “consistent” with those emitted by an airplane’s black box, the leader of the multinational search operation said Monday.

Although officials cautioned that they had not confirmed the plane’s location, the signals mark the most promising lead in a month-long search for Malaysia Airlines Flight 370, which disappeared March 8 with 239 passengers and crew members on board. If the acoustic noises ultimately lead searchers to the missing Boeing 777, the timing of this breakthrough is extraordinarily fortunate: The batteries powering the plane’s emergency beacons are likely to run out within hours or days.

Retired Air Chief Marshal Angus Houston said at a news conference in Perth, Australia, that the noises are “probably the best information we’ve had” so far.

Houston said the vessel, the Ocean Shield, picked up the signals on two occasions Sunday — once for more than two hours, a second time for 13 minutes. On the second occasion, two distinct noises were detected, which would be expected if both the flight data recorder and the cockpit voice recorder are emitting signals.

It could take days to determine whether the acoustic noises are coming from what’s left of Flight 370, thought to be at the bottom of the Indian Ocean. Confusing matters, a Chinese patrol ship on Friday and Saturday detected signals of its own, about 300 nautical miles from where the Australian vessel is positioned. Officials say it’s unlikely that the signals detected by the two vessels came from the same source.

Compare the depth of Malaysia Airlines Flight 370 to other milestone depths and distances.

For at least the next day, the Ocean Shield will continue its slow runs over the small area where it has picked up the acoustics. The goal, Houston said, is to pinpoint the most likely location of the sound. If that can be done, search crews plan to lower an ­autonomous underwater vehicle onto the three-mile-deep ocean floor on Tuesday to search for wreckage and map out a possible debris field. The process could be arduous, because the ocean depths are at the limit of the vehicle’s capability.

“This is not the end of the search,” Houston said. “We’ve still got a lot of difficult, painstaking work to do to confirm this is the spot where the aircraft entered the water. The best evidence we could get is imagery from the autonomous vehicle suggesting that the aircraft is on the bottom of the ocean.”

If wreckage is found on the ocean floor, searchers will require months to map its location and bring it to the surface.

“In very deep oceanic water, nothing happens fast,” Houston said.

False leads and scant data have hampered the search for the plane, which flew in its final hours through a remote area virtually uncovered by radar. Investigators have tried to piece together the airliner’s likely crash site by analyzing communications the plane made with a satellite while airborne. Both the Australian vessel and the Chinese patrol ship have been operating along the arc that represents a best guess of the plane’s last known position.

Although the latest signals provide a tantalizing clue, investigators say they are still desperate to find physical evidence of the plane’s whereabouts. On Friday, search teams began using underwater equipment to scan for black-box transmissions. More than two dozen ships and airplanes have been scouring a broad section of the Indian Ocean well off the western coast of Australia.

The Ocean Shield, using black-box detection equipment provided by the U.S. Navy, picked up a signal in a relatively northern part of that search area, about 1,050 miles northwest of Perth.

A black box emits high-frequency signals that can create a complicated pattern of sound waves under the surface.

Still, the plane may not necessarily be directly below the spot where the signal was detected. Sound waves behave curiously underwater, bending based on the water’s temperature, pressure or salinity. The sound waves, in some instances, can travel great distances laterally, said Commodore Peter Leavy of the Royal Australian Navy.

“It is a markedly different environment than what you see with sound traveling through air,” Leavy said.

The Ocean Shield is outfitted with a beaklike device called a pinger locator that is dropped into the water and then dragged on back-and-forth runs. Although the search area is huge, the Ocean Shield is focusing on a three-by-three-mile section where it detected the signals Sunday. When dragging the pinger locator, the vessel moves only a few miles per hour, and pulling a U-turn takes three hours, given the complex network of cables it is towing. One out-and-back run takes seven hours, Leavy said.

Normally, the pinger locator glides through the water at a depth of about 9,800 feet, or nearly two miles. But when the Ocean Shield first picked up a signal Sunday, the pinger was positioned closer to the surface — about 1,000 feet.

Australian and U.S. Navy members aboard the ship switched off a series of whirring electronic devices to reduce noise, said Cmdr. William Marks, a spokesman for the U.S. Navy’s 7th Fleet. The pinger locator was then dropped to about 5,000 feet. Those aboard then heard the sound for more than two hours.

“As the Ocean Shield moved through the water, signal got stronger, stronger, stronger, then weaker, weaker, weaker,” Marks said by telephone from a command ship stationed in Yokosuka, Japan. “That’s exactly how you’d expect it if it was the black box.”

Houston said Tuesday that the crew of the Ocean Shield won’t yet deploy the autonomous underwater vehicle, a 16-foot submarine-like device called the Bluefin-21, hoping first to detect another transmission from the depths.

If functional in the three-mile depths, the Bluefin can use sonar to map out a debris field. But when operating along the ocean floor, it is “literally crawling,” Houston said.

“We need another transmission to further refine the area” where the Bluefin will be used, he said.

Officials involved in the search say they have grown more optimistic that wreckage from the aircraft will eventually be recovered. The flight, a red-eye from Kuala Lumpur, Malaysia, bound for Beijing, inexplicably veered from its flight path less than an hour after takeoff in what Malaysian officials describe as a deliberate act by somebody on board.

Investigators have revealed little about the criminal probe into the pilots and passengers. But even if the black box is recovered, the mystery of what happened aboard the aircraft might not be resolved. The cockpit voice recorder keeps only two hours of the latest audio, meaning that critical events shortly after takeoff — when the plane was first steered off course — were overwritten as the airliner headed south toward the Indian Ocean.