All 20 children who died in a shooting at a school in Connecticut were aged between six and seven, according to an official list of the dead. The state's chief medical examiner said the gunman used a rifle as his main weapon, and all the victims appeared to have been shot several times. The gunman, named in media reports as Adam Lanza, killed his mother before driving to the school and opening fire. Six adults, all women, were also killed before the gunman shot himself dead. The head teacher at Sandy Hook school in Newtown, Dawn Hochsprung, is listed among the dead, along with adults Rachel DaVino, Anne Marie Murphy, Lauren Russo, Mary Sherlach and Victoria Soto. The youngest child to be killed was Noah Pozner, who celebrated his sixth birthday only last month. Most of the children who died on Friday were girls and nearly all were aged six. A woman who worked at the school was the only person to be shot and survive. Obama to visit Earlier on Saturday, Lt Paul Vance of Connecticut state police said the gunman had forced his way into the school, and had not been let in "voluntarily". He said investigators had gathered "good evidence" in the search for a motive, without elaborating. President Barack Obama is to visit Newtown on Sunday to meet families and speak at a vigil. After the attack, he urged "meaningful action" against gun crime in the US. "As a country we have been through this too many times," he said in an emotional White House address. The gunman killed his mother at the home they shared before driving to the school in her car and opening fire. Reports say the guns used in the attacks were registered to her. There are conflicting reports about whether she had worked at the school in the past. Connecticut Chief Medical Examiner H Wayne Carver said the gunman shot all the victims at the school with a semiautomatic rifle, at least some of them from close range. Asked how many shots were fired, he replied: "I'm lucky if I can tell you how many I found." Initial reports suggested that the killer had used two handguns which he also had with him. The suspected gunman's father, Peter Lanza, said his family was "struggling to make sense of what has transpired". "Our family is grieving along with all those who have been affected by this enormous tragedy," he said in a statement. Connecticut Governor Dannel Malloy made a television address saying the children were "taken from their families far too soon". "What's important right now is love, courage and compassion," he said. 'Absolutely quiet' Friday's killings took place in two rooms within a single section of the school, police have said. The shooting lasted just a few minutes. As they heard the shots, teachers in other parts of the building tried to protect children by locking doors and ushering them into closets. "I told them we had to be absolutely quiet, because I was just so afraid if he did come in, then he would hear us and just start shooting the door," said teacher Kaitlin Roig. "I said to them, 'I need you to know that I love you all very much and that it's going to be okay', because I thought that was the last thing they were ever going to hear."