Aerial photo taken on March 28, 2018 shows a man watching karst caves inside a sinkhole in Zhenxiong County, southwest China's Yunnan Province. Altogether six sinkholes are found 51 kilometers away from the Zhenxiong County, which take up about 600 mu (about 40 hectares). The biggest sinkhole has a diameter of about 600 meters and an average depth of 120 meters. (Xinhua/Hu Chao)