At least 14 newborn babies have died in a fire on a hospital ward in Pakistan's capital Islamabad.The fire broke out on the third floor of the mother and child unit of the Pakistan Institute of Medical Sciences (PIMS) hospital, one of the main state-run hospitals in the city, on Wednesday morning.An air conditioning unit caught fire, a spokesman for the hospital told the BBC. There were 15 babies in the ward when the fire broke out, a hospital spokesman said. One baby was rescued. The babies in the ward were either in incubators or hooked on oxygen equipment, Pakistan's Health Minister Mustafa Kamal told Geo News. Oxygen is not flammable on its own, but it can accelerate a fire, making materials burn hotter and faster.Pakistan's Prime Minister Shehbaz Sharif has suspended Federal Secretary of Health Aslam Ghauri, a top official in the health department, removing him from his post.The PM has been chairing a high-level meeting on the hospital fire, and has expressed "deep anger" at some officials, the information ministry said.Eyewitnesses described chaotic and harrowing scenes at the hospital, including intense smoke and broken glass, with some complaining that rescuers were slow to respond.One of them, Khurram Mehmood, told the AFP news agency his three-day-old daughter died in the fire and claimed that rescuers took hours to arrive: "We were sitting on the road waiting for help."Another witness, Abdul Ghafoor, told AFP the fire spread "very quickly".He said he went into the hospital to try to help save patients but could not reach the maternity ward: "There was thick black smoke inside and patients were trapped... rescue teams arrived after almost two hours."Hivsa Walid told the BBC she was inside the hospital when the fire broke out, with her sister-in-law who had given birth in the days before. She said they were in the nursery opposite the room where the fire started. They heard a shout and initially thought someone had died but then saw the smoke. They grabbed the baby - who is so young she's not yet been named - and ran.The newborn babies who died in the fire have been badly burnt, and will need to be identified in through DNA tests, police said. Only after the DNA tests can the bodies be returned to their parents. Emergency responders rescued at least 19 other people from the hospital, including 10 women, seven children and two men.Prime Minister Sharif expressed his "deep sorrow and heartfelt regret" over the hospital fire, and instructed the authorities to "conduct an immediate investigation", according to the statement from his office."Such a situation with children is irreparable", the statement said. Islamabad's District Magistrate has formed a fact-finding committee to investigate the fire which must produce a report "within 24 hours".