The China Eastern Airlines Corp. jet that crashed Monday was traveling at close to the speed of sound in the moments before it slammed into a hillside, according to a review of flight-track data.

Such an impact may complicate work for investigators because it can obliterate evidence and damage a plane’s data and voice recorders that are designed to withstand most crashes. The cockpit voice recorder was located Wednesday, officials in China said.

According to data from Flightradar24, a website that tracks planes, the Boeing Co. 737-800 was knifing through the air at more than 640 miles (966 kilometers) per hour before hitting the ground and at times may have exceeded 700 mph.