According to admittedly sketchy and incomplete reports, on the morning of June 4, 2013, a Air China Boeing 757 on route from Chengdu to Guangzhou was flying at an altitude of 26,000 feet when suddenly it was struck by an unknown flying object. The collision occurred 20 minutes after takeoff, soon after the aircraft reached cruising altitude. There were no injuries aboard the aircraft but the Boeing 757 suffered major damage to the nose cone of the aircraft. Pilots chose to turn back to the airport in Chengdu where they made an emergency landing, stepped outside, and were stunned to see the extensive damage caused to the plane by the collision.
Some speculated that the collision was a bird strike while others argued that the altitude was much too high for birds. In addition, photographs of the damaged cone show distinct black and gray scrape marks on the paint, unusual markings not typically seen with bird strikes (which leave, eh, splats).
Check out the pictures below.