The search for the missing Malaysian jetliner MH370 is now in its 31st day. Chinese search and rescue ship Haixun 01 has picked up two signals which match the frequency of the plane's black box pinger.

Australian ship Ocean Shield has also picked up two similar underwater signals. Investigators are calling these their "most promising lead" yet and efforts have been doubled to verify their source.

The search effort is also continuing on the ocean surface. 12 planes and 14 ships were searching three designated zones on Monday, one of which overlaps with the Ocean Shield's underwater search. In the press conference held on the same day, Malaysia's Acting Transport Minister Hishamuddin Hussein said he is "cautiously hopeful" that there will be positive developments in the next few days, "if not hours," in the search for the missing airliner.

The Malaysian Acting Transport Minister also denied CNN reports suggesting the jetliner had veered north of Indonesia before turning toward the southern Indian Ocean to avoid radar detection.

Authorities have also warned that it will take time to confirm whether the sounds are signals from the flight data recorders that belonged to Malaysia Airlines Flight 370, which vanished a month ago. The batteries in the black boxes run out after about 30 days, so searchers are in a race against time to locate the devices.