Media playback is unsupported on your device Media caption Oceanographer Dr Simon Boxall: "If this is the pulse, this becomes a viable search"

A Chinese ship searching for the missing Malaysia Airlines plane in the southern Indian Ocean has picked up a pulse signal, Chinese media say.

They say the signal has a frequency of 37.5kHz - the same as those emitted by the flight recorders.

However there is no evidence so far that it is linked to MH370.

Dozens of ships and planes have joined the search, with the operation moving into its most intensive phase before batteries on the data recorders fade.

On Saturday the Haixun 01 - one of two Chinese ships in the area - picked up the signal at about 25 degrees south latitude and 101 degrees east longitude, the state-run Xinhua news agency said.

"It is yet to be established whether it is related to the missing jet," it cautioned.

Media playback is unsupported on your device Media caption Richard Westcott reports on the use of a pinger locator to find a black box

China's Liberation Daily reported that three people on board had heard the signals, which were not recorded as they came suddenly.

Image copyright Reuters Image caption Officials said there was "some hope" the locators would be able to find the black box

The head of the Australian agency co-ordinating the search said the reported signals "are consistent with the aircraft black box" but "there is no confirmation at this stage that the signals and the objects are related to the missing aircraft".

The flight is believed to have crashed in the southern Indian Ocean, although no confirmed debris has been found.

Analysis This could be potentially significant, but caution is necessary. There have been many apparently promising leads over the past few weeks that have looked like the search team closing in, only for those leads to turn into nothing. The tantalizing element is the frequency of the signal supposedly picked up. It is consistent with a black box pinger. But we know very little more about the nature of the contact. The Chinese ship is not among those that have been mentioned before as having special equipment to search for the black box pinger, but it is a very modern search-and-rescue vessel. Even with the sophisticated listening devices now being deployed in the search, the size of the search area, the range of the pinger signal, and the depths of water involved all mean it would need a lucky break at this stage to detect a signal.

It is still not known why the plane diverted from its planned flight path from Kuala Lumpur to Beijing four weeks ago with 239 people on board.

Race against time

Two of the ships searching an area of about 217,000 sq km (84,000 sq miles) have underwater locator capabilities.

Australian naval vessel Ocean Shield is using a "towed pinger locator" from the US Navy, while HMS Echo, which has similar capabilities, is also searching.

They are trying to detect an underwater signal emitted by the data recorders.

The battery-powered signal fades after 30 days.

The area - about 1,700km (1,000 miles) north-west of Perth - has been picked on the basis of analysis of the satellite data.

On Saturday, Malaysia announced it had set up three ministerial committees to help co-ordinate the search, and a new investigation team which would include members from Australia, China, the US, the UK and France.