Haixun 01, searching for the Malaysia Airlines Flight MH370, detected a pulse signal with a frequency of 37.5kHz per second in southern Indian Ocean waters today, state-run Xinhua news agency reported.
It is yet to be established whether it is related to the Boeing 777-200, that went missing on March 8 with 239 people on board, including five Indians.
A black box detector deployed by the Haixun 01 picked up the signal at around 25 degrees south latitude and 101 degrees east longitude, the report said.
The batteries of the black box flight recorders have a life of about 30 days, meaning they will shut down in the next three days.
Officials said the multinational team has entered the most intensive phase in the search operations.
Up to 10 military planes, three civil jets and 11 ships were searching about 217,000 sq km, 1,700 km north west of Perth, to locate the plane's data recorder that could help investigators unravel the mystery of what happened on March 8, the day the Beijing-bound jet suddenly disappeared from radar screens.
China's Liberation Daily reported that three people on board had heard the signals, which were not recorded as they came suddenly.
The frequency of 37.5 kHz per second is currently the international standard for the underwater locator beacon on a plane's black box.
Also, a Chinese air force plane searching for the jet spotted a number of white floating objects in the search area today.
The plane photographed the objects over a period of 20 minutes after spotting them at 11:05 local time.
An Australian pilot on board the plane reported the information to the Joint Agency Coordination Center (JACC), which is coordinating the massive multinational search in the southern Indian Ocean.
The plane was the first to leave Perth International Airport for the day's search schedule today. It arrived at the designated area, about 2,700 kilometres from Perth, this morning.
JACC said in a statement that the weather forecast for today's search is fair, with possible showers in the search area.
However, Xinhua reported that search conditions were difficult with gales of 4-5 m/sec, waves of 1 to 2 metres and a cloud ceiling of about 200 metres.
Earlier today, Malaysia vowed it will not give up on efforts to search the missing airliner.
Acting Transport Minister Hishammuddin Hussein told reporters in Kuala Lumpur the cost of the ongoing search was immaterial as compared to giving solace to the families of people on board the ill-fated plane.
"I can only speak for Malaysia, and Malaysia will not stop looking for MH370," Hishammuddin said, adding the search will continue "with the same level of vigour and intensity."
In line with international agreements, Malaysia will appoint an independent investigator to lead an international team to probe what happened to MH370, he said.
The team will include Australia, China, the US, Britain and France.