At least 21 students and a teacher were killed after the roof of a school collapsed in Pakistan‘s Peshawar city on Thursday.Twenty students and a female teacher were killed and more than 40 people injured in the incident, officials said.Peshawar Capital City Police chief Mian Saeed said the incident occurred in Dir Colony in the city’s inner area, as cited by PTI.Lady Reading Hospital spokesperson Muhammad Asim said an emergency had been declared at the facility to treat the injured.All the children killed in the incident were aged 13 or younger, Asim said. Rescue officials said 25 injured children had been taken to medical facilities.Rescue teams were clearing the debris and searching for children and school staff who might still be trapped beneath the collapsed structure.Pakistan Prime Minister Shehbaz Sharif expressed deep grief over the loss of life and extended his condolences to the bereaved families.Building and roof collapses are common in Pakistan, largely due to poor safety standards and the use of substandard construction materials.In July, three girls aged between three and 13 were killed when part of the outer wall of a government primary school near Umerkot collapsed, burying them under the debris, as cited by Dawn.That same month, a child was killed and at least five others were injured when the roof of an under-construction private school building collapsed in Lahore’s Baghbanpura neighbourhood.In June, 14 children died after the roof of a private tuition centre collapsed in Lahore’s Kahna area. Less than two months earlier, four children were killed and 20 people injured when a classroom roof collapsed at a private school in Dera Ghazi Khan.