"The suspect in the bus has surrendered to officers, and is in custody," the Las Vegas Metropolitan Police Department said on its Twitter account.
Police spokesman Larry Hadfield earlier told reporters the shooting had ocurred on the bus.
"We had one single shooting incident with two victims. Both were transported to the trauma center and one is deceased," USA Today quoted Hadfield as saying.
The suspect, a man believed to be in his 50s, was riding on the second floor of a double-decker bus when he opened fire "indiscriminately," assistant sheriff Tom Roberts said, the Las Vegas Review Journal reporters.
Aerial photos showed police vehicles surrounding the white bus. Police deployed two robots, which were reported to have been used to remove a window on the bus.
Witnesses tweeted that police used loudspeakers to negotiate with the suspect.
Earlier in an unrelated incident, as many as three robbers wearing animal masks - one tweet showed a person wearing a pink pig mask - used sledgehammers to break into a jewelry case in a store in the high-end Bellagio Hotel.
The suspects in that incident wore black suits or tuxedos, police Lieutenant Carlos Hank told the Las Vegas Journal-Review.
"It's like a movie," he said. "It's just crazy."
Police attributed initial reports of an active shooter to people hearing the sound of the glass in jewelry cases being broken. But that proved to be false.
The luxury resort was briefly put on lockdown, and at least one person was taken into custody.