Authorities have yet to declare the number of victims, but there has been no sign so far that any of the 132 people onboard had survived.
Investigators still do not know why the plane suddenly entered a near-vertical dive in southern China on Monday.
But the recovery of the intact cockpit voice recorder is hoped to yield clues.
The black box was found damaged on the outside but its internal records appeared to be fine, officials said. It has been sent to Beijing for its data to be analysed.
Search teams found the first of the crucial black boxes in difficult circumstances on Wednesday.
Heavy rains have flooded the steep and rugged landscape of the crash site in Wuzhou, making efforts harder for hundreds of rescuers and volunteers, who have so far also found scattered plane debris and the charred remains of personal belongings.