A gunman killed at least 50 people and wounded more than 400 at a country music festival on the Las Vegas Strip on Sunday, raining down rapid fire from the 32nd floor of a hotel for several minutes before he was shot dead by police.

The death toll, which police emphasized was preliminary, would make the attack the deadliest mass shooting in US history, eclipsing last year's massacre of 49 people at an Orlando night club.

Thousands of panicked people fled the scene, in some cases trampling one another as law enforcement officers scrambled to locate and kill the gunman. Shocked concertgoers, some with blood on their clothes, wandered the streets after the attack.

Police identified the gunman as area resident Stephen Paddock, 64, and said they had no information yet about his motive.

He was not believed to be connected to any militant group, Clark County Sheriff Joseph Lombardo told reporters.

"We have no idea what his belief system was," Lombardo said. "We've located numerous firearms within the room that he occupied."

Authorities believed they had located Paddock's roommate, who they identified as Marilou Danley. He gave no details of whether she was suspected of involvement in the attack but described her as an "associate."

Police had located two cars that belonged to the suspect.

The dead included one off-duty police officer, Lombardo said. Two on-duty officers were injured, including one who was in stable condition after surgery and one who sustained minor injuries, Lombardo said. Police warned the death toll may rise.