TEHRAN, Sept. 18 (Xinhua) -- At least 51 people were injured on Thursday in a fire at a commercial-residential building in Iran's northeastern Razavi Khorasan province, state-run IRIB news agency reported. The incident occurred at a seven-story building in Sabzevar city, and all those injured were taken to the hospital, IRIB quoted Reza Chaman, head of Sabzevar University of Medical Sciences, as saying. He added that five of the wounded are in critical condition. Abbas Masoumi-Sadr, head of the city's fire department, said firefighters and rescuers were sent to the scene, noting that the building's height made containing the fire very difficult. He added that the cause of the incident was under investigation.