For more than 2,000 years, Dunhuang in China's northwestern Gansu province was known as a pearl of the ancient Silk Road – famous for its oasis with a crescent-shaped lake and “singing sand” dunes. But today, Dunhuang is under threat from the expanding Kumtag Desert. Experts say without urgent efforts to protect Dunhuang, the city which continues to have great importance for archaeology and tourism, could disappear in 50 years.