After detecting signals possibly from the black box of the missing Malaysian plane, China’s search vessels failed to find any confirmed clues today to conclusively establish that the pings are from the MH370.

Vessels of China’s ministry of transport searching for the missing passenger jet have searched a total of 136,000 square kilometres by midday on Sunday, Zhuo Li, an official with the China Maritime Search and Rescue Center, said.

The centre had mobilised 62 merchant ships for their assistance in the search, he said.

Haixun 01 of the ministry and two Navy vessels continued the underwater search in southern Indian Ocean, three other ships were searching on the water surface. Two other vessels were searching in eastern Indian Ocean, Mr. Zhuo was quoted by official Xinhua news agency as saying.

China pressed 18 vessels, eight helicopters and three fixed-wing aircraft to trace the plane missing since March 8, along with 239 people on board.

Earlier in the day, three separate but fleeting sounds from deep in the Indian Ocean offered new hope in the hunt for the missing Malaysian airliner, as officials rushed to determine whether they were signals from the plane’s black boxes before their beacons fall silent.

The head of the multinational search being conducted off Australia’s west coast confirmed that a Chinese ship had picked up electronic pulsing signals twice in a small patch of the search zone, once on Friday and again on Saturday.

On Sunday, an Australian ship carrying sophisticated deep-sea sound equipment picked up a third signal in a different part of the massive search area.

“This is an important and encouraging lead, but one which I urge you to treat carefully,” retired Australian Air Chief Marshall Angus Houston, who is coordinating the search, told reporters in Perth.

“We have an acoustic event. The job now is to determine the significance of that event. It does not confirm or deny the presence of the aircraft locator on the bottom of the ocean,” Mr. Houston said, referring to each of the three transmissions.

China’s official Xinhua News Agency reported on Saturday that the patrol vessel Haixun 01 on Friday detected a “pulse signal” at 37.5 kilohertz (cycles per second) the same frequency emitted by flight data recorders aboard the missing plane in the southern Indian Ocean.

The British Navy ship HMS Echo, which is fitted with sophisticated sound-locating equipment, is moving to the area where the signals were picked up and will be there in the next day or two, Houston said.

The Australian navy’s Ocean Shield, which is carrying high-tech sound detectors from the U.S. Navy, will also head there, but will first investigate the sound it picked up in its current region, about 300 nautical miles (555 kilometres) away, he said.

Australian air force assets are also being deployed into the Haixun 01’s area to try to confirm or discount the signals’ relevance to the search, Houston said.

In Kuala Lumpur, families of passengers aboard the missing plane attended a prayer service on Sunday that also drew thousands of Malaysian sympathizers.

“This is not a prayer for the dead because we have not found bodies. This is a prayer for blessings and that the plane will be found,” said Liow Tiong Lai, the president of the government coalition party that organized the two-hour session.

Two Chinese women were in tears and hugged by their caregivers after the rally. Many others looked somber, and several wore white T-shirts emblazoned with the words “Pray for MH370”.

Two-thirds of the passengers aboard Flight 370 were Chinese, and a group of relatives has been in Kuala Lumpur for most of the past month to follow the investigation. Mr. Liow said some of them were planning to go home on Sunday.

After weeks of fruitless looking, the multinational search team is racing against time to find the sound-emitting beacons and cockpit voice recorders that could help unravel the mystery of the plane. The beacons in the black boxes emit “pings” so they can be more easily found, but the batteries last for only about a month.

Investigators believe Flight 370 veered way off-course and came down somewhere in the southern Indian Ocean, though they have not been able to explain why it did so.

The crew of the Chinese ship reportedly picked up the signals using a hand-held sonar device called a hydrophone dangled over the side of a small runabout something experts said was technically possible but extremely unlikely.

The equipment aboard the Ocean Shield and the HMS Echo are dragged slowly behind each ship over long distances and are considered far more sophisticated than those the Chinese crew was using.

Footage aired on China’s state-run CCTV showed crew members in the small boat with a device shaped like a large soup can attached to a pole. It was hooked up by cords to electronic equipment in a padded suitcase as they poked the device into the water.

“If the Chinese have discovered this, they have found a new way of finding a needle in a haystack,” said aviation expert Geoffrey Thomas, editor-in-chief of AirlineRatings.com. “Because this is amazing. And if it proves to be correct, it’s an extraordinarily lucky break.”

There are many clicks, buzzes and other sounds in the ocean from animals, but the 37.5 kilohertz pulse was selected for underwater locator beacons because there is nothing else in the sea that would naturally make that sound, said William Waldock, an expert on search and rescue who teaches accident investigation at Embry-Riddle Aeronautical University in Prescott, Arizona.

“They picked that (frequency) so there wouldn’t be false alarms from other things in the ocean,” he said.

But after weeks of false alarms, officials were careful on Sunday not to overplay the development.

“We are hopeful but by no means certain,” Australian Prime Minister Tony Abbott said of the detection of the signals.

“This is the most difficult search in human history. We need to be very careful about coming to hard and fast conclusions too soon,” Mr. Abbott told reporters during a visit to Japan.

The agency was formally told about the second Chinese detection on Saturday “in absolutely the normal way”, he said.

“China is sharing everything that is relevant to this search. Everything,” Mr. Houston said.

Still, the search agency will be adding a Chinese-speaking liaison officer “to make sure nothing falls through the cracks,” he said.

The signals detected by the Chinese ship were in the southern high priority zone, Mr. Houston said.

Up to 12 military and civilian planes and 13 ships took part in the search on Sunday of three areas totalling about 216,000 square kilometres (83,400 square miles). The areas are about 2,000 kilometres (1,200 miles) northwest of the Australian west coast city of Perth.

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