LAS VEGAS — There was chaos at Mandalay Bay Hotel and Casino as SWAT teams used explosives to get into the hotel room where the suspect behind the deadliest mass shooting in modern U.S. history was inside.

The gunman perched on the 32nd floor of a Las Vegas casino last night, unleashing a shower of bullets on an outdoor country music festival below and killing at least 50 people as tens of thousands of concertgoers ran for their lives. More than 400 victims have been taken to the hospital, authorities said.

SWAT officers using explosives stormed the gunman’s hotel room and found he had killed himself, authorities said.

There was no immediate word on the motive for the attack. The U.S. Homeland Security Department said there was no “specific credible threat” involving other public venues in the U.S.

Country music star Jason Aldean was performing Sunday night at the end of the three-day Route 91 Harvest Festival in front of a crowd of 22,000 when the gunman opened fire from inside the Mandalay Bay Hotel and Casino.

The gunman was identified as Stephen Craig Paddock, 64, of Mesquite, NV.

Two Canadians who witnessed a mass shooting at an outdoor concert in Las Vegas say that at first, they thought the sound of gunshots was fireworks.

Monique Dumas of B.C. says she was six rows from the front of the stage when the shooting broke out.

She says she thought she heard a bottle breaking, and then a burst of popping sounds she thought was fireworks.

Ashley Fowler of Newfoundland told the radio station K-Rock in St. John’s, N.L., that everyone in the crowd thought the noise was fireworks until the performer on stage dropped his microphone and ran.

Global Affairs Canada did not immediately respond to a request for comment on the number of Canadians who may have been affected by the shooting.

According to the Las Vegas Visitor Authority, visitors from Canada made up nearly half of international tourists who arrived in the city by air last year.

As the bullets ran rampant, thousands in the crowd fled in every direction. Dumas said it was “organized chaos” as everyone fled. “It took four to five minutes and all that time there was gunfire.”

In addition to Paddock, police said they located a woman who may have been his roommate: Marilou Danley, 62.

Police shut down the usually busy Las Vegas Boulevard and authorities across the state and federal ranks converged on the scene as dozens of ambulances ferried those struck by gunfire. Nearby Interstate 15 and flights at McCarran International Airport were briefly closed.

Air Canada has revised its ticketing policy for customers booked on affected flights to facilitate changes to bookings, in effect all day today, Oct. 2. “Those customers wishing to make alternate travel arrangements can do so without penalty, space permitting, using our online rebooking tool: check your alternate travel options currently available; re-book yourself and check in before arriving at the airport. Prior to leaving for the airport, please check your Flight Status, or call Air Canada’s automated flight information system at 1-888-422-7533. Air Canada Vacations Customers must contact Air Canada Vacations directly for rebooking or for travel alternatives at 1-800-296-3408.”

WestJet is advising all passengers travelling to or from Las Vegas Oct. 2 – 4 to check the status of their flight prior to leaving for the airport.

Jose Baggett, 31, of Las Vegas, said he and a friend were in the lobby of the Luxor hotel-casino – directly north of the festival – when people began to run, almost in a stampede.

He said people were crying and as he and his friend started walking away minutes later, they encountered police checkpoints where officers were carrying shotguns and assault rifles.

“There were armoured personnel vehicles, SWAT vehicles, ambulances, and at least a half-mile of police cars,” Baggett said.

With files from The Associated Press and The Canadian Press