A US official says Las Vegas shooter Stephen Paddock reported at least a dozen gambling transactions of $10,000 or more in the past several weeks.

The official also said Tuesday that Paddock had transferred $100,000 to the Philippines in the days before the attack that killed 59 people at a country music concert.

The official said investigators are still attempting to trace that money.

The official, who was briefed by law enforcement, wasn't authorised to publicly discuss an ongoing investigation and spoke to The Associated Press on condition of anonymity.

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Leaked photographs from inside the hotel room used by Las Vegas shooter Stephen Paddock showing his arsenal of weapons. Photo / Breaking911 Twitter
Leaked photographs from inside the hotel room used by Las Vegas shooter Stephen Paddock showing his arsenal of weapons. Photo / Breaking911 Twitter

The person also said investigators are focusing more attention on what the girlfriend of Paddock may have known about the attack.

Federal investigators are expected to question Marilou Danley when she returns to the US on Wednesday.

Meanwhile off-duty Las Vegas area firefighters who were attending the country music festival when a gunman opened fire on the crowd say they immediately started setting up makeshift triage operations with concertgoers bringing them gunshot victims.

Firefighters Benjamin Kole and Anthony Robone say Sunday night's concert suddenly transformed into a horrific massacre.

Kole says victims' injuries ranged from bullet wounds to sprained ankles.

Flowers and candles are left at a makeshift memorial site on Las Vegas Boulevard. Photo / AP
Flowers and candles are left at a makeshift memorial site on Las Vegas Boulevard. Photo / AP

Most of those who were shot were hit in their heads or upper bodies.

Robone says he taught people with no medical training how to use belts as tourniquets to stop victims from bleeding. Other people used poles and tarps make gurneys.

Kole and Robone described their experiences to reporters on Tuesday.

Union officials say 12 off-duty firefighters were shot while attending a country music festival in Las Vegas, including two who were wounded while administering CPR to gunshot victims.

Angelo Aragon, president of the Professional Fire Fighters of Nevada, said Tuesday that all the firefighters survived their wounds.

Debris litters a festival grounds across the street from the Mandalay Bay resort and casino. Photo / AP
Debris litters a festival grounds across the street from the Mandalay Bay resort and casino. Photo / AP

Clark County Fire Chief Greg Cassell says none of the 108 on-duty firefighters from around the region who tended the wounded was injured.

He says one of the wounded off-duty firefighters was from Las Vegas. Others were from places around the country.

Aragon says several of them described sending loved ones away from the scene as they set up triage stations and taught concertgoers to help provide emergency care such using belts as tourniquets.

Anthony Robone of the Henderson fire department said he did first aid on his older brother Nicholas who was shot in the upper chest. The brother is in stable condition.

Former first lady Michelle Obama is expressing her condolences over the mass shooting that left 59 people dead at a concert in Las Vegas.

A broken window is seen at the Mandalay Bay resort and casino. Photo / AP
A broken window is seen at the Mandalay Bay resort and casino. Photo / AP

She reflected Tuesday on how difficult it was for her and her husband to try to comfort the nation when such attacks occurred.

Obama said her heart goes out to the victims and their families because too much of the job of being commander in chief is overseeing that kind of loss and not having a solution to offer the families.

Obama was interviewed by television producer Shonda Rhimes at the Pennsylvania Conference for Women in Philadelphia.

Some of the worst mass shootings in U.S. history occurred during former President Barack Obama's eight-year term, including the 2016 attack at an Orlando, Florida, nightclub that left 49 people dead and the 2012 massacre at a school in Newtown, Connecticut, that killed 20 children and six adults.

People embrace on the Las Vegas Strip. Photo / AP
People embrace on the Las Vegas Strip. Photo / AP

In further news, the company that owns the Mandalay Bay casino-resort is donating $3 million to help victims of the shooting in Las Vegas.

MGM Resorts International on Tuesday announced the donation.

Gunman Stephen Craig Paddock opened fire from a room at Mandalay Bay on a crowd of concertgoers.

Mandalay Bay chief executive officer Jim Murren said in a statement the company hopes the donation will make a difference to those who were harmed and those who are left behind.

He says the company also wants to recognize first responders.

The company says the money will fund humanitarian assistance to victims and organizations that help those who are first on the scene to assist in traumatic events.

Longtime Las Vegas entertainer Wayne Newton and his wife donated $100,000 to a victims' fund.

- AP