One of the two black boxes belonging to the ill-fated China Eastern Flight 5735, carrying 123 passengers and nine crew members, has been found, the country said on Wednesday.

Rescue teams had previously been forced to temporarily suspend the difficult search in a remote mountain area of the Guangxi Zhuang Autonomous Region, because of unsafe conditions caused by rain.

The black box, which is key to finding out what happened in any plane crash, is severely damaged. Its recorder is so damaged that investigators are not able to tell whether it is the flight data recorder or the cockpit voice recorder, officials said.

The plane which left Kunming bound for Guangzhou, a flight done successfully dozens of times in the last year, inexplicably fell from the sky in a huge fireball on Monday.

As family members gathered at the destination and departure airports, what caused the plane to drop out of the sky shortly before it would have begun its descent to the southern China metropolis of Guangzhou remained a mystery.

The second black box has yet to be found.

All 132 people who were onboard are presumed dead. Rescuers have found personal effects like wallets and luggage but have yet to find any survivors in the challenging terrain.