At least 17 people have been killed in a mass shooting at a high school in southern Florida, police said Wednesday, according to dpa. Scott Israel, the sheriff of Broward Country, said 12 victims were found dead inside the school building, two others were found outside and a further victim was found in a nearby street. He added that two others died of their injuries after being transported to local hospitals. The 19-year-old suspect, identified as Nikolaus Cruz, opened fire with an AR-15 rifle at Marjory Stoneman Douglas High School in Parkland, Florida, after setting off a fire alarm. He had been expelled from the school "for disciplinary reasons," Israel said. "It's catastrophic. There really are no words," Israel said. Cruz was in custody, but the scene at the Parkland school - some 75 kilometres north of Miami - was "still active," the Broward Country sheriff's office said on Twitter. A total of 17 people, including the shooter and the two who later died, were taken to hospital, according to Evan Boyar, a doctor at Broward Health North hospital. Pupils were evacuated to a nearby school and TV footage showed them leaving campus buildings in single file. Footage also showed SWAT teams entering the campus and rescue workers loading people into ambulances. Local media described the male shooter as wearing a black hat and a burgundy-coloured top. CBS Miami showed aerial footage of a man fitting that description with his hands behind his back, surrounded by officers next to a police vehicle. According to non-profit organization Everytown, there have been 17 school shootings in the United States since the beginning of the year. US President Donald Trump said he had spoken Florida Governor Rick Scott and that the White House is working with law enforcement "on the terrible Florida school shooting." "No child, teacher or anyone else should ever feel unsafe in an American school," he wrote on Twitter.