Officials said there was an explosion and fire at a power station in the rear of the Monte Carlo resort.
Clark County fire officials did not confirm the source of the blast.
There were no immediate reports of injuries.
The Monte Carlo experienced another fire in January 2008, with flames caused by flying molten metal devouring a foam-like building material on the 32-story resort. Thousands of guests and employees were evacuated, but no serious injuries were reported. The resort's owners, MGM Resorts International, refurbished and reopened the rooms on its top floor.
The Associated Press contributed to this report.