"The towed pinger locator deployed from the Australian defence vessel Ocean Shield has detected signals consistent with those emitted from aircraft black boxes," said Joint Agency Coordinating Centre chief Angus Houston, emphasising that further confirmation was needed.
He said the Ocean Shield detected the first signal lasting 2hrs 20 mins while the second for 13 mins at the northern part of the search area.
He cautioned that the search and rescue could not confirm what the signals were from until the aircraft wreckage is found.
"This is very encouraging information which unfolded in the last 24 hours," he told a daily press briefing here on Monday.
Houston said the sounds were heard at a depth of 4,500 meters (about 14,764 feet), adding it could take days before officials can confirm whether the signals did indeed come from the plane.
"Nothing happens fast," Houston said, adding he was much more optimistic in finding the plane than he was a week ago.
"I would like us to find some wreckage," he added.