A man opened fire about 5:45 a.m. wounding a manager and a guard at Drai's After Hours, a club at Bally's hotel-casino, police Sgt. John Sheahan said. Another guard might have been injured.
Sheahan said the nightclub was open at the time and the shooter was believed to have acted alone. He was hospitalized with unspecified injuries.
Sheahan said the male patron was fatally wounded trying to subdue the gunman as people ran from the club.
"The person is in custody. The weapon is in custody," Sheahan said. "There are no outstanding suspects in this incident."
Three people were taken by ambulance to University Medical Center, where spokeswoman Danita Cohen said one died and two remained in critical condition.
Their names weren't immediately made public.
Sheahan said the gunman is expected to face murder and multiple attempted murder charges.
Authorities said he paid the cover charge then demanded his money back before opening fire.
The club has a capacity of about 500 people and charges $30 for entry, said Celena Haas-Stacey, a spokeswoman for Bally's hotel owner Caesars Entertainment Corp.
Sheahan said the gunman told employees the crowd Monday morning was so small that he wanted his money back.
A manager was shot in the arm during the argument and a security officer who wrestled with the gunman was also shot before the patron joined the melee, Sheahan said.
Gambling continued in most of the casino after the shooting. Yellow crime scene tape stretched around several banks of slot machines just outside the club. Debris littered the carpeted floor.
The entrance is located on the casino level of Bally's near a drive-up entrance off Flamingo Road near Las Vegas Boulevard.
The club, open Thursdays through Mondays from 1 a.m. to 9 a.m., has been an after-hours attraction at the heart of the Strip since the late 1990s. It moved earlier this year from the former Bill's Gamblin Hall, which is undergoing renovations, to Bally's across the street. Drai's is expected to move back to the renamed site next year.
Both properties are owned by Caesars Entertainment. The company issued a statement offering sympathies to victims and deferred questions to police.
The intersection of Flamingo Road and Las Vegas Boulevard was the scene of a shooting and fiery crash last February involving a self-described pimp. Authorities say he exchanged words with a man outside another Strip casino then fired shots from his Range Rover into a moving Maserati, mortally wounding the driver and triggering a crash with a taxi that left two other people dead.
A death penalty trial in that case is scheduled to begin Dec. 2, but could be delayed by a change of defense attorneys.