There was a flash of light and smoke appeared to come from the bus.
No information has been made available as of early Saturday evening regarding the identities of the suspect or the victims.
This is the second shooting incident to occur in less than 24 hours in Sin City, as a gunman in a pig mask opened fire during an armed robbery at the iconic Bellagio hotel earlier in the day.
That gunman opened fire during an armed robbery at the nearby Bellagio hotel, prompting terrified tourists to seek shelter amid a chaotic scene.
At least three people entered a high-end store, which is believed to be a Rolex store, inside the resort, including one who fired gunshots, police said.
This is the second gunman incident to occur in less than 24 hours in Sin City, as a gunman in a pig mask opened fire during an armed robbery at the iconic Bellagio hotel earlier in the day.
Las Vegas SWAT officers surround a bus along Las Vegas Boulevard. Photo / AP
Larry Hadfield, a spokesman with Las Vegas Metro police, said of the bus situation to USA Today: "The shooting incident happened on the bus. We had one single shooting incident with two victims. Both were transported to the trauma center and one is deceased."
Hadfield added that SWAT and hostage negotiation personnel are on site but wouldn't confirm if there were passengers still on the regional transit bus.
Witnesses and photos suggest the day's earlier armed burglary took place at the Bellagio's Rolex store, and show a person in a pig mask with a gun in hand.
One suspect has been taken into custody.
Guests and tourists had to flee the hotel and head out to the strip amid report of the armed robbery.
Panicked people have tweeted their shock, with one woman saying she had to hide under a table.
No one was injured, Las Vegas Metropolitan Police Department later confirmed. Parts of the casino property remain closed as authorities investigate.
Officers received a call about the incident at the Bellagio at 12:50 am, and has apprehended one suspect by 2:15 am, the Las Vegas Review-Journal reported.
One woman who was at the hotel when the robbery unfolded described the atmosphere as one of 'mass panic'.
One Twitter user posted a chilling image of a man wearing one of the masks standing outside the store, prompting fears that a robbery was under way. Photo / Twitter
"Everyone running. I'm currently ducked on the floor under a table," she wrote.
The store was closed when the armed robbers got in and all shots were fired inside, police said.
Some witnesses said the burglars used sledgehammers to break into the store, although police have not confirmed it so far.
