Shares in PetroChina, the overseas-listed unit of China’s largest energy company, surged on Friday on confirmation of one of the world’s largest oil and gas discoveries of recent times in shallow waters in Bohai Bay near the port city of Tianjin.

PetroChina said that it had confirmed in principle “proven reserves” of oil of 405m tonnes, or about 3bn barrels, and gas of 111m tonnes of oil equivalent.