UPDATE: The gunman has been identified as 64-year-old Stephen Paddock.

Las Vegas authorities have now said there are over 50 people dead and over 200 injured after Paddock opened fire at the Mandalay Bay Resort.

The Nevada Senator Dean Heller is calling the Las Vegas mass shooting a "senseless, horrifying act of violence."

Police responded to reports of the shooting just after 10 p.m. (1 a.m. ET), and the suspect was fatally shot in the Mandalay Bay Resort and Casion, officials said.

Authorities found several weapons in Paddock’s room after using explosives to enter, law enforcement officials reported. It was not immediately clear what kinds of weapons were found.

At least one off-duty Las Vegas police officer was shot, Lombardo said. Several other off-duty police officers are believed to be among the dead and injured.

Meghan Kearney described the chaotic scene.

“We heard what sounded like firecrackers going off. Then all of a sudden we heard what sounded like a machine gun. People started screaming that they were hit… When we started running out there were probably a couple hundred [people] on the ground,” she told MSNBC.

"People kept dropping and dropping. … People were getting shot one foot away from us," she said. “People were trying to save their friends. There were gunshots everywhere. Helping them would’ve meant that we got shot, too.”

Police have located Paddock’s roommate, Marilou Danley, 62, for questioning, Lombardo said. They also found two vehicles related to the investigation: a Hyundai Tuscon and a Chrysler Pacifica Touring, both with Nevada license plates.

Earlier, police shut down the area and urged the public to stay away. Flights in and out of the airport were temporarily halted.

Aldean, who was named the Academy of Country Music's Entertainer of the Year in April 2017, was on stage performing on the final night of the three-day Route 91 Harvest festival at the Las Vegas Village when the first shots rang out.

Aldean later said via Instagram that he and his band were safe.

PREVIOUS STORY: The Las Vegas sheriff says officers have killed the gunman on 32nd floor of the hotel across from outdoor concert.

The sheriff says more than 20 people are dead and more than 100 people are injured from the concert attack.

The Nevada sheriff says off-duty officers attending Las Vegas country music festival have died.

Multiple people were injured in after a shooting in Las Vegas near Mandalay Bay Resort and Casino Sunday, Clark County Fire Department officials confirmed to NBC News.

Las Vegas police said they were investigating reports of an active shooter near or inside the casino.

Mandalay Bay is located on the south end of the Vegas strip on Las Vegas Boulevard and across from McCarran International Airport.

Police shut down Las Vegas Blvd and urged the public to stay away. Flights were being held in and out of the airport.

The final night of the Route 91 Harvest Music Festival was taking place across the street from Mandalay Bay when the reported shooting took place.

Jon Bessette said he was attending the Rout 91 music festival when he heard gunshots around 10:00 p.m. "The band ran off stage and it was pandemonium," Bessette said. "Everyone was running, people were getting trampled."

Several artists performing at the music festival also reported hearing gunshots.

This is a developing story. Please check back for updates.