A fire on the roof of the Monte Carlo hotel-casino forced guests and gamblers to flee today.
It sent a plume of smoke above the Las Vegas Strip before easing about an hour later, hotel officials said.
No major injuries were reported, said Clark County spokesman Eric Pappa.
The fire, which was reported around 11am local time (7pm Irish time), halted gambling at the casino as it spread from the centre of the building across the roof.
Fiery debris fell to the street below, and orange flames lapped at the casino's sign.
Officials went door to door evacuating the hotel, said Gordon Absher, a spokesman for the resort's owner, MGM Mirage.
Larry Wappel, 25, of San Pierre, Indiana, said he and his brother, Eric Wappel, were in a room on the 30th floor when they heard housekeeping staff banging on doors and yelling "Fire, get out!"
He said it took about 10 minutes to walk single-file down the stairs to get to ground level.
"There were a couple of ladies crying, but it was pretty calm," he said.
Another guest, Renza Badilla, 45, said she exited through the hotel kitchen to find burning debris and embers falling from the roof.
"I think people were shocked when they saw the smoke," Ms Badilla said.
Investigators were trying to determine whether the fire had simply burned the resort's facade or penetrated rooms in the upper floors, which contain suites.
Guests were being taken to the MGM Grand Garden Arena and employees were evacuated to the adjacent New York-New York hotel, Mr Absher said.
Huge crowds formed to watch the fire and traffic on the Las Vegas Strip was gridlocked as streets were blocked off around the hotel.
The nearby resorts Bellagio and New York-New York were not evacuated.
The Monte Carlo Resort & Casino has 3,002 guest rooms and 211 suites.
The resort, located on Las Vegas Boulevard, near Tropicana Avenue, opened in June 1996.
The 32-storey casino-hotel modelled after the Place du Casino in Monte Carlo, Monaco, was a joint venture between Steve Wynn's Mirage Resorts and Circus Circus Enterprises.