The signal had a frequency of 37.5kHz per second -- identical to the beacon signal emitted by flight recorders, the official Xinhua news agency said.
A black box detector deployed by the Chinese search ship Haixun 01 picked up the signal at about 25 degrees south latitude and 101 degrees east longitude, Xinhua said.
It is yet to be established whether the signal detected by Haixun 01 was related to the missing jet.
Malaysian authorities believe satellite readings indicate MH370 crashed in the Indian Ocean, far off Australia's western coast, after veering dramatically off course during a flight from Kuala Lumpur to Beijing on March 8. But no proof has yet been found that would indicate a crash site.
Authorities still have no idea how or why the plane vanished, and warn that unless the black box is found, the mystery may never be solved.