At least 21 people have been killed and 61 others injured after a powerful explosion tore through a fireworks factory in central China, according to state media.The blast struck a workshop at the Huasheng Fireworks Manufacturing and Display Company in Liuyang, Hunan province, at around 4.40pm on Monday. The county-level city, under the provincial capital Changsha, is known for its large-scale fireworks production.Chinese President Xi Jinping called for “all-out efforts” to locate those still missing and ensure the injured receive urgent treatment. Footage shared online showed thick white smoke billowing high above the site shortly after the explosion.