A British man who identified himself as the father of gunman Chris Harper-Mercer, who opened fire at a college in the US state of Oregon killing nine people, told reporters on 1 October he was "shocked" by his son's involvement, adding that it had been a "devastating day".

Speaking to a group of reporters outside of his home in Tarzana, California, Ian Mercer said he would not answer questions, but confirmed that he is the father of 26-year-old British-born Chris Harper-Mercer, who lived only a few miles from the Umpqua Community College, where he opened fire on students before being shot dead by police.

"Obviously, it's been a devastating day. Devastating for me and my family," said Mercer. "I'm just as shocked as everybody at what happened today. I've just been talking to the police and the FBI. That's all the details I have right now, is what you know already," he said.

The massacre in Roseburg, a former timber town in Umpqua River Valley, is the latest in a series of mass shootings at US college campuses, movie theatres, military bases and churches in recent years. It is the deadliest incident since June when a gunman attacked worshippers at a South Carolina church killing nine.