Three students have been killed in an explosion in a laboratory at Beijing Jiaotong University, the capital’s fire services said. The incident happened at around 9.30am on Wednesday when the students, from the urban planning and environmental engineering department, were carrying out sewage treatment experiments in a laboratory building on the east campus, the fire services said in a statement. “The incident caused the death of three students who participated in the experiment,” the statement said. The cause of the incident was not immediately known and the authorities were investigating. 8 killed, 22 hurt as knife-wielding man hijacks bus in southeast China Video footage circulating online showed the building was engulfed in dark smoke while flames were also visible. Eight fire crews and 30 fire engines were sent to tackle the blaze. Some students told The Beijing News that they were taking an exam in a neighbouring building and heard an explosion before the room started filling with smoke. They were then told to evacuate the building. One student said she heard several loud bangs after leaving the building A statement from the university said the fire was brought under control within an hour and there were no other casualties. The area has been sealed off for investigation. Other students at the university expressed their shock and offered condolences to friends and families of the victims. “It is easy to neglect safety in university laboratories,” said one social media user, who said they hoped the incident would lead to better safety standards. “May the deceased rest in peace. Safety is more important. Please protect yourselves when doing scientific research,” wrote another. The incident happened just a month after a laboratory explosion in which a lecturer and several students were injured at the Nanjing University of Chinese Medicine in Taizhou. In December 2015, a 32-year-old postgraduate student was killed when a hydrogen cylinder exploded during a laboratory experiment at Tsinghua University in Beijing.