A child was among four people killed in a shooting at a Southern California office building that left a fifth victim and the gunman critically wounded, police said. The violence in the city of Orange southeast of Los Angeles was the nation's third mass shooting in just over two weeks. When police arrived at the two-storey structure around 5:30 p.m on Wednesday, shots were being fired, Orange Police Lt. Jennifer Amat said. Officers opened fire and the suspect was taken to a hospital, Amat said. It's unclear if the suspect suffered a self-inflicted wound or was shot by police. Police provided no details on the victims other than to say one was a child and a woman was critically wounded.