Police stand guard outside the Mandalay Bay Resort & Casino following a mass shooting which killed 50 people. Mark Ralston/AFP/Getty Images

At least 58 people died and 515 more were injured after a shooting at an outdoor music festival in Las Vegas last night. The gunman, 64-year-old James Paddock, opened fire from the 32nd floor of the Mandalay Bay Resort and Casino during a Jason Aldean concert. The attack was the deadliest mass shooting in American history.

While many details of the shooting are still being assessed, one of its most immediate effects was on the New York Stock Exchange. MGM Resorts International, which owns the Mandalay Bay, was down nearly three percent in early trading. Shares dropped as much as five percent overnight but had rebounded slightly by the opening bell.

“Our hearts and prayers go out to the victims of last night’s shooting, their families, and those still fighting for their lives,” MGM Chairman and CEO Jim Murren said in a statement. “We are working with law enforcement and will continue to do all we can to help all of those involved.”

Fellow casino owner Wynn Resorts, Ltd. was down about one percent early in the day, after falling two percent overnight.

Las Vegas Sands was down almost two percent in premarket trading, but soon after the NYSE opened for business stocks were actually slightly up.

MGM Resorts International MGM, +9.32% is reopening more resorts in Las Vegas over the next few weeks. Luxor and The Shoppes at Mandalay Bay Place will open their doors again June 25 at 10 a.m.

Mandalay Bay Casino Stock

• Background Location. The Las Vegas Strip is a stretch of Las Vegas Boulevard immediately south of the city of Las Vegas in Clark County, Nevada.The Strip is known for its concentration of casinos and resort hotels, including the 43-story Mandalay Bay southwest of its intersection with Mandalay Bay Road, in the unincorporated town of Paradise. Las Vegas Village, a 15-acre (6.1-hectare) lot.
• The 14 civil complaints, filed together in state court in Las Vegas, follow at least three others filed since Paddock opened fire Oct. 1 from the 32nd floor of the Mandalay Bay hotel and casino.
• BetMGM Sportsbook at Mandalay Bay. The world-famous Mandalay Bay sportsbook is the one and only place Resortists go to play and watch the action. The world-famous Mandalay Bay sportsbook is the one and only place resortists go to play and watch the action.

The casino stock selling spree follows a period of growth in the market. MGM was up 13 percent for the year after Friday’s close, while Wynn stock has jumped 72 percent, and Las Vegas Sands shares are up 20 percent.

Mandalay Bay Casino Host Directory

Paddock, who died from a self-inflicted gunshot wound at the scene of the shooting, had an arsenal of 20 rifles in his hotel room. While it’s not clear yet exactly what kinds of firearms he used, shares in most gun manufacturers were up early in the day.

Sturm, Ruger & Company stock increased nearly five percent soon after the opening bell, while shares in American Outdoor Brands, which owns Smith & Wesson, were up just over five percent.

Casino mogul Steve Wynn says the gun massacre outside the Mandalay Bay casino isn't keeping tourists away from Las Vegas.

'If you're going to ask us what effect did the tragedy at Mandalay have on us? None that we can measure,' Wynn said late Thursday on a conference call to discuss his company's earnings.

Profit at Wynn Resorts(WYNN) topped Wall Street forecasts, thanks to solid sales at casinos in Las Vegas and Macau, a Chinese territory where gambling is legal.

But the attack in Las Vegas earlier this month, which left 58 people dead and almost 500 injured, got much of the attention on the conference call.

Wynn said his company has invested more in security since the shootings. He expects the rest of the industry is doing the same.

'We're sort of operating as a group. Some of us are talking to one another, like the Sands and MGM,' he said.

Wynn said people 'in every executive suite up and down The Strip and in Reno and everywhere else and in hotels around the country' are searching for ways to prevent another massacre.

'We've had programs of training our employees for two years -- room service, housekeeping, audio visual people that go to fix a TV or touch screen,' Wynn said.

'They've all been trained for two years. They inspect the rooms. They look at the people. We profile everybody,' he added.

Wynn said that the Las Vegas gunman, Stephen Paddock, had been a gambler at Wynn-owned casinos since 2006 but that there was nothing remarkable about him. He was a typical slots and video poker player who 'didn't owe a dime in Las Vegas,' Wynn said.

'He didn't meet the profile of a problem gambler or anything like that. He was a very controlled person,' Wynn said.

Casino workers who knew Paddock 'were stunned, mystified, that the person they knew could have been a person that tried to assassinate hundreds and thousands of people,' Wynn said.

Other Las Vegas companies have also said business is getting back to normal.

Las Vegas Sands(LVS), which also operates in Macau, reported solid results and a healthy forecast. And Boyd Gaming(BYD), which owns several casinos in downtown Las Vegas, echoed Wynn's comments about strong tourism.

Boyd CEO Keith Smith said his company does not 'anticipate any material impact' on visitors to Vegas in the near future.

Caesars Entertainment(CZR) and Mandalay owner MGM(MGM) wlll release their latest earnings in early November.