Some of the first officers to reach the Las Vegas hotel room where a gunman unleashed the deadliest mass shooting in modern US history busted in with shields and found his body and assault-style weapons scattered around, according to police body-camera video.

Hours of footage from two officers’ body-worn cameras show police walking into a casino that was still packed after gunfire started raining down on an outdoor concert from 32 floors up in a Las Vegas Strip casino-hotel.

People were still playing slot machines as an officer told an employee: “There’s a shooter. He’s shot and killed multiple people already.”

Police ordered people to flee and told a worker: “Get everyone out of here.”

Police say Stephen Paddock killed 58 people and injured hundreds more as he fired for 10 minutes from the windows of his hotel suite in October before killing himself as authorities closed in.

The videos do not provide a complete view of everything police discovered when they entered Paddock’s suite or any clues about why he opened fire on October 1.

The footage shows officers checking rooms in the Mandalay Bay before getting to Paddock’s room.

An officer says, “Breach! Breach! Breach!” before a loud bang and a fire alarm begins to sound.

Inside, Paddock’s body is seen, wearing dark trousers, a long-sleeve shirt, and a glove on his left hand.

An apparent pool of blood stains the carpet near his head as a police Swat officer walks past.

In the footage, an officer grabs an assault-style rifle from the ledge of a broken window and other weapons are found around the room.

The videos record officers talking about whether there is evidence of a second shooter and finding Paddock’s driving licence.

Police and the FBI later said they believe the 64-year-old former accountant and high-stakes video poker player acted alone.

The videos do not show what the first officer through the door saw because he did not activate his body-worn camera. The disclosure by police lawyers late on Tuesday raised questions about whether officers followed department policy.

Officers searching hallways during the deadliest mass shooting in modern US history Credit: AP

The newly released videos represent a sample of hundreds of hours of body-camera recordings, none of which offer a motive for the shooting, Clark County Sheriff Joe Lombardo told reporters on Tuesday.

The police investigation is not finished, said Mr Lombardo, the elected head of the Las Vegas Metropolitan Police Department.

He called the preparation and release of the information sought by media outlets in a public records lawsuit a “monumental task” that diverts resources from police work.

“What is seen on those videos in no way changes the facts that we were able to clarify for you shortly after the crime,” Mr Lombardo said.

He referred to a preliminary police report released on January 19 that said Paddock meticulously planned the attack, researched police Swat tactics, rented hotel rooms overlooking outdoor concerts and investigated potential targets in at least four US cities.

Mr Lombardo’s top spokeswoman, Carla Alston, said on Wednesday that no one in the agency would comment about whether the first officer through the door followed proper procedure by not turning on his camera or whether he had been disciplined for violating policies.

The department requires officers with body cameras to activate them during calls that lead to interaction with residents and searches.

Department lawyers told a judge that there were almost 750 hours of body-camera recordings and volumes of 911 audio recordings.

More footage is set to be released in the coming weeks.