news.sina.com.cn/o/2018-07-12/doc-ihfefkqr2429480.shtml
news.sina.com.cn/c/2018-07-13/doc-ihfhfwmu9113462.shtml
From the sources above:
2018年7月10日，国航CA106航班执行香港至大连航班任务。在巡航阶段，飞机出现座舱高度警告，机组人工释放了旅客氧气 面罩，并实施紧急下降，于北京时间22：31分在大连机场安全落地，机上153名旅客， 9名机组成员，无人员受伤，飞机没有受损。
"July 10, 2018, flight AirChina CA106 was en route from Hong Kong to Dalian. During the cruise, there was a cabin altitude warning, and the crew has manually released the passenger oxygen masks and performed an emergency descent. The plane landed safely at Dalian airport at 22:31 Beijing Time, there were no injuries among all the 153 passengers and 9 crew members. The plane was also intact".
知情人士爆料，7月10日国航CA106航班机组在飞行途中抽烟，误把两个组件当成再循环风扇关掉导致座舱释压，飞机宣布May day紧急下降；机组在发现问题后，打开组件增压并在氧气不符合适航条件下又重新上升到7500米高度继续飞往目的地。
According to sources, the crew of CA106 on July 10th was smoking during flight, and mistakenly turned off two components that they thought were recirculation fans, which led to pressure-release from the cabin. The plane declared "Mayday" and performed an emergency descent. Once the crew has identified the problem, they turned the component back on, and ascended to 7500 meters to the destination under the oxygen condition that's not suitable for cruising.
“机舱温度升高，整个空调系统好像停了。”一位乘客王先生说。当时机舱内广播通知：“飞机可能失密，正在紧急下降，请保持安静， 系好安全带。”
"The temperature was raising in the cabin, and the entire A/C system seemed to be turned off" - A passenger Mr. Wang said. The cabin announcement: "it's possible that the plan has lost its seal, and we are performing an emergency descent, please stay calm and fasten your seatbelt."
Another source:
news.sina.com.cn/o/2018-07-13/doc-ihfhfwmu5229093.shtml
经过初步调查，系副驾驶因吸电子烟，为防止烟雾烟味弥漫到客舱，在未通知机长的情况下，实际上想关循环风扇，错误地关闭了相邻空 调组件，导致客舱氧气不足，客舱高度告警。
According to preliminary investigation, it's caused by the co-pilot smoking e-cigarette. To keep the smoke and smell away from the passenger cabin, the co-pilot, without informing the captain, with the intention of turning off the recirculation fan, but mistakenly turned off the A/C component located next to it, which led to insufficient oxygen in the cabin and cabin altitude warning.