A gunman has shot dead two members of a news crew live on air in Virginia.

CBS News has said that that reporter Alison Parker and videographer Adam Ward for CBS Roanoke affiliate group WDBJ-TV died from the assault during a broadcast early on Wednesday morning.

During the interview at Smith Mountain Lake in Moneta, the camera was dropped amid gunfire and screams could be heard. The broadcast cut back to a stunned news anchor.

Graphic footage of the attack has emerged on Facebook and Twitter.

US media outlets quoted the governor of Virginia as saying the gunman was an ex-employee.

#breakingnews Virginia governor says suspected shooter is disgruntled former employee of TV station. He is currently being pursued by police — Brad Bell (@ABC7Brad) August 26, 2015

At the time of publication, the gunman remains at large.

Official confirms to me that the person being interviewed in WDBJ's live shot, Vicki Gardner, was "shot in the back & in surgery right now." — Brian Stelter (@brianstelter) August 26, 2015

It is with extreme sadness that we report WDBJ7's Alison Parker and Adam Ward were killed in an attack this morning. http://t.co/oC9s4vLJXV — WDBJ7 (@WDBJ7) August 26, 2015

We love you, Alison and Adam. pic.twitter.com/hLSzQi06XE — WDBJ7 (@WDBJ7) August 26, 2015

The gunman, a Vester Lee Flanagan II, was live-tweeting the murder from his Twitter account. The social network very quickly deleted the account but not before his first person footage of the shooting was autoplayed on the streams of many users.