Three signals that could be from the black box of Malaysia Air Flight 370 were heard this weekend, the most promising lead in the search for the missing plane so far.

On Saturday, the Chinese ship Haixun 01 detected a pulse signal of the same frequency as that used by black boxes. Later that day, the ship detected another one in the same location, this time lasting for 90 seconds. A third signal was heard by an Australian ship, though in a different location -- about 300 nautical miles and 24 hours away, according to the New York Times. It's doubtful the two ships could be hearing the same signal. False pings can and do happen -- last week, for example, the HMS Echo got a false ping.

None of these reports have been verified, though search ships are rushing to the area of the Haixun 01 in the hopes that they soon will be.  

Angus Houston, who is coordinating the search, said the signals were "an important and encouraging lead." Australian Prime Minister Tony Abbott said he was "hopeful but by no means certain."

But Houston also urged caution, noting that if Haixun 01 was close to the black box, it should receive an uninterrupted pulse signal -- "not just a fleeting encounter." And there are doubts that the black box detector technology used by the Chinese is even powerful enough to hear signals from as deep into the ocean as the plane would be -- nearly three miles in that area. The New York Times says the Haixun 01 is using a pinger locator intended to be used by divers in much shallower water. It's supposed to be held in a diver's hand, but the Chinese have mounted it onto a pole that is then stuck in the water off the side of the ship. An expert said it was "possible, but not probable" that the Haixun 01's technology could pick up the black box signal.

"If it proves to be correct, it's an extraordinarily lucky break," aviation expert Geoffrey Thomas told the AP.

The Australian ship that detected the other signal is equipped with a much more sophisticated ping locator.

Day 30 of the search for Flight 370 is Monday. It is around this time that the black box's batteries will die -- and with them, the hope that the plane will be located any time soon.