An oil tank exploded at a chemical plant in Urumqi, capital of northwest China's restive Xinjiang region, on Sunday morning, the official Xinhua News Agency reported quoting firefighters. No casualties have been reported so far and the cause is being investigated, the report said. The explosion occurred around 10 a.m. at a refinery of China National Petroleum Corp. in northern Urumqi, Xinhua quoted city firefighters as saying.