Twenty children and six adults have been killed in a shooting attack at a primary school in the US state of Connecticut, police say.Lt Paul Vance said the gunman was also dead, but did not identify him.However, officials told US media the killer at Sandy Hook Elementary School, Newtown, was a 20-year-old son of a teacher at the school.Newtown is now one of the worst school shootings in US history, after 32 died at Virginia Tech in 2007.Early reports named 24-year-old Ryan Lanza as the gunman, but anonymous officials later said his brother Adam, 20, was the suspect.Ryan Lanza was being questioned by police, the Associated Press and New York Times reported.Lt Vance said 18 children were pronounced dead at the school, and two died after they were taken to hospital. Six adults were also killed. The gunman died at the scene.According to US reports, the gunman's mother was a teacher found among the dead at the school.One person was also injured, and police were investigating a "secondary" crime scene, where another victim was found dead, Lt Vance said.He gave no details, but said New Jersey police were providing assistance.Dressed in black and wearing a bullet-proof vest, the gunman is thought to have had several weapons at the school, although it is not clear whether he used more than one.The attack took place in two rooms within a single section of the school, police have said.Night has fallen in Newtown, and school officials announced that a memorial service would take place at 19:00 EST (00:00 GMT).