KUALA LUMPUR/PERTH, Australia (Reuters) - A Chinese patrol ship hunting for a missing Malaysia Airlines jetliner detected a pulse signal in the south Indian Ocean on Saturday, the state news agency Xinhua reported, in a possible indicator of the underwater beacon from a plane's "black box".
A black box detector deployed by the vessel Haixun 01 picked up the "ping" signal at around 25 degrees south latitude and 101 degrees east longitude, according to Xinhua.
It has not been established whether the ping is related to Flight MH370, which went missing four weeks ago with 239 people aboard shortly after taking off from Kuala Lumpur for Beijing.
Xinhua further said a Chinese air force plane spotted a number of white floating objects in the search area.
Australian search authorities also said they had yet to verify whether the pulse signal was related to MH370.
Malaysia said earlier on Saturday it had begun a formal investigation into the jet's March 8 disappearance that would comprise experts from around the world, while the huge hunt for the Boeing 777 airliner intensified in the Indian Ocean.
Normally, a formal air safety investigation is not launched until wreckage is found. But there have been concerns that Malaysia's informal investigations to date have lacked the legal standing of an official inquiry convened under U.N. rules.
Authorities have not ruled out mechanical problems as a cause but say the evidence, including the loss of communications, suggests Flight MH370 was deliberately diverted thousands of kilometers (miles) from its scheduled route.
Defense and acting Transport Minister Hishammuddin Hussein told a news conference that Australia, China, the United States, the United Kingdom and France had agreed to send representatives to take part in the investigation.
The extensive search and rescue operation has so far included assets from around 26 countries.
Under International Civil Aviation Organisation rules, the country where the aircraft is registered leads the investigation when the incident takes place in international waters.
A spokesman from the U.N. agency told Reuters that it received official notification of the accident on 28 March, meaning that the investigation was considered officially launched on that date.
Hishammuddin said that the investigation would be made up of three groups: An "airworthiness" group would examine maintenance records, structures and systems; an "operations" group would study flight recorders, operations and meteorology; and a "medical and human factors" group would look into psychology, pathology and survival factors.
The Malaysian government has also set up ministerial committees to oversee everything pertaining to the next of kin of the passengers and crew on board the aircraft, the appointment of the investigation team and the deployment of assets in the search operation.
EXTENSIVE SEARCH CONTINUES
Searchers on Saturday launched the most intensive hunt yet in the southern Indian Ocean, trying to find the plane's black box recorders before their batteries run out.
Up to 10 military planes, three civilian jets and 11 ships were scouring a 217,000-sq-km (88,000-sq-mile) patch of desolate ocean some 1,700 km (1,060 miles) northwest of Perth, Australia near where investigators believe the Boeing went down.
"If we haven't found anything in six weeks we will continue because there are a lot of things in the aircraft that will float," Retired Air Chief Marshal Angus Houston, the head of the Australian agency coordinating the operation, told reporters.
"Eventually I think something will be found that will help us narrow the search area."
Dozens of flights by a multinational taskforce have so far failed to turn up any trace of the plane.
The Boeing 777 was briefly picked up on military radar on the other side of Malaysia and analysis of subsequent hourly electronic "handshakes" exchanged with a satellite led investigators to conclude the plane crashed far off the west Australian coast hours later.
Sonar equipment on two ships joining the search may help find the plane's black box voice and data recorders that are key to unlocking what happened on the flight. The black box is equipped with a locator beacon that transmits "pings" when underwater, but its batteries may only last 30 days.
Australian authorities said the so-called Towed Pinger Locator will be pulled behind navy ship HMAS Ocean Shield, searching a converging course on a 240-km (150-mile) track with British hydrographic survey ship HMS Echo.
Experts have warned the Towed Pinger Locator may be of little use unless investigators can get a much better idea of exactly where the plane went into the water, because its limited range and the slow speed at which it must be pulled behind the ship mean it cannot cover large areas of ocean quickly.
"I won't even call it an area. What we are doing is we are tracking down the best estimate of the course that the aircraft was on," U.S. Navy Captain Mark Matthews told Reuters. "It takes a couple of days on each leg so its a slow-going search."
Britain is also sending HMS Tireless, a Trafalgar-class nuclear submarine with sonar capabilities, and a Malaysian frigate was due to arrive in the search area on Saturday.
Malaysian authorities have faced heavy criticism, particularly from China, for mismanaging the search and holding back information. Most of the 227 passengers were Chinese.