Twenty-one people have been killed and 61 others injured after an explosion occurred at a fireworks manufacturing plant in Liuyang city, Hunan province, Chinese state media reported on Tuesday.The blast took place around 5 pm on Monday at Liuyang Huasheng Fireworks Manufacturing and Display Co, a fireworks plant located at Guandu township, state-run Xinhua news agency reported.Emergency and fire rescue teams were pressed into service and deployed at the site shortly after the explosion.In the incident, 21 people have died and 61 others have been admitted to hospital for treatment.