MGM Resorts International has experienced a "cybersecurity issue" that has resulted in computer outages at properties across the United States.
The company tweeted an announcement on Monday, stating that it "shut down certain systems" and an investigation is ongoing.
"MGM Resorts recently identified a cybersecurity issue affecting some of the Company’s systems. Promptly after detecting the issue, we quickly began an investigation with assistance from leading external cybersecurity experts. We also notified law enforcement and took prompt action to protect our systems and data, including shutting down certain systems. Our investigation is ongoing, and we are working diligently to determine the nature and scope of the matter," the tweet read.
All computer-based operations are being done manually and the outage is even impacting credit card machines, according to a FOX 5 Las Vegas report.
The interruption began at about midday on Sunday as websites for all MGM Resorts International locations went offline.
The incident impacted reservation systems and casino floors in Las Vegas and states including Maryland, Massachusetts, Michigan, Mississippi, New Jersey, New York and Ohio was not immediately known, company spokesman Brian Ahern said.
Some visitors at Aria, an MGM Resorts property in Las Vegas, Nevada, said that even slot machines were not working and a few guests were unable to get into their rooms on Sunday night using their digital key cards, according to 8 NewsNow.
The current MGM Resorts website is unavailable, however, they still have a landing page where customers can contact the concierge at each property for more assistance.
The company has tens of thousands of hotel rooms in Las Vegas at properties including the MGM Grand, Bellagio, Cosmopolitan, New York-New York, Park MGM, Excalibur, Luxor, Mandalay Bay and Delano.
It also operates properties in China and Macau.
The Associated Press contributed to this report. This story was reported from Los Angeles.