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 US, 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 UN 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.-Reuters