Shares of Las Vegas casino operators fell as much as 5 percent in premarket trading on Monday after a gunman killed at least 50 people and wounded 200 others in a mass shooting on the Las Vegas strip.

MGM Resorts International, which owns the Mandalay Bay hotel from where the gunman opened fire, was down 5 percent. Melco Resorts & Entertainment Ltd., Wynn Resorts Ltd. and Las Vegas Sands Corp. each fell 1 to 2 percent.

In a statement on Twitter, MGM Resorts said it had locked down hotels in the vicinity at the request of law enforcement officers. It was unclear if other casinos were also put on lockdown following the incident.

“Our thoughts and prayers are with the victims of last night’s tragic events. We’re grateful for the immediate actions of our first responders,” MGM Resorts said in the tweet.

Our thoughts & prayers are with the victims of last night's tragic events. We’re grateful for the immediate actions of our first responders. pic.twitter.com/RsrFDkp5WW

— MGM Grand Hotel (@MGMGrand) October 2, 2017

Las Vegas’s casinos, nightclubs and shopping draw some 3.5 million visitors from around the world each year and the area was packed with visitors when the shooting broke out shortly after 10 p.m. local time.