A Mandalay Bay maintenance worker says he alerted the hotel to the Las Vegas gunman before Stephen Paddock began firing from his window into concertgoers below.

Mandalay Bay employee Stephen Schuck told NBC News on Thursday morning (AEST) he was checking a report of a jammed fire door on the 32nd floor of the hotel and casino when he heard gunshots and a security guard, who had been shot in the leg, told him to take cover.

The revised timeline has renewed questions about whether police could have reached the 64-year-old Paddock’s room in time to prevent some of the 58 deaths caused by his prolonged barrage into the concert crowd.

“As soon as I started to go to a door to my left, the rounds started coming down the hallway,” Mr Schuck said. “I could feel them pass right behind my head.

“It was kind of relentless, so I called over the radio what was going on,” he said. “As soon as the shooting stopped we made our way down the hallway and took cover again and then the shooting started again.”

Mr Shuck’s claims come after police said Tuesday they believe Paddock shot an unarmed hotel security guard, Jesus Campos, through the door of his suite six minutes before he opened fire on the concert.

That account differs dramatically from the original sequence of events presented by police last week, which stated Paddock injured the Mr Campos after shooting into the crowd.

It is now thought Mr Campos used his radio and possibly a hallway phone to also call hotel dispatchers for help.

MGM Resorts International, which owns Mandalay Bay has questioned the new timeline.

“We cannot be certain about the most recent timeline,” MGM’s Debra DeShongwas was quoted as saying by AP. “We believe what is currently being expressed may not be accurate.”

Las Vegas police did not respond to US media requests Thursday morning (AEST) to questions about the hotel’s statement.

“Our officers got there as fast as they possibly could and they did what they were trained to do,” Las Vegas assistant sheriff Todd Fasulo told AP on Wednesday.

The AP reported that gunshots can be heard in the background as Mr Schuck called in the shooting on his radio, telling a dispatcher: “Call the police, someone’s firing a gun up here. Someone’s firing a rifle on the 32nd floor down the hallway.”

It was unclear if the hotel relayed the information to Las Vegas police, who did not respond to questions about whether hotel security or anyone else in the hotel called 911 to report the gunfire.

Joseph Giacalone, a professor at John Jay College of Criminal Justice and a retired New York City police sergeant told the AP the new timeline “changes everything”.

“There absolutely was an opportunity in that timeframe that some of this could’ve been mitigated,” he said.

Las Vegas Sheriff Joseph Lombardo originally said police officers reached the 32nd floor within 12 minutes of the first reports of the attack.

That sequence of events was changed on Monday.

“What we have learned is (the security guard) was encountered by the suspect prior to his shooting to the outside world,” Sheriff Lombardo said.

Sheriff Lombardo did not address whether the mass shooting could have been prevented, or halted sooner, based on the new chronology, but said it remained unclear why Paddock stopped firing on the concert when he did.

Nevada Lieutenant Governor Mark Hutchison acknowledged to CNN on Tuesday that Paddock did not stop firing because of Mr Campos, as had been assumed initially.

Mr Campos immediately alerted the hotel’s in-house security team after he was shot at 9:59 pm, six minutes before Paddock first opened fire on the concert, according to Lombardo.

– With agencies