Police believe an altercation earlier at an unspecified casino resort prompted the car-to-car attack in the heart of the Strip at Las Vegas Boulevard and Flamingo Road.
The crossroads is the site of several major hotel-casinos, including Bellagio, Caesars Palace and Bally's.
"This doesn't happen where we come from, not on this scale," said Mark Thompson, who was visiting from Manchester, England, with his wife. "We get stabbings, and gang violence, but this is like something out of a movie. Like `Die Hard' or something."
Police said they were contacting authorities in three neighboring states about the Range Rover Sport with dark tinted windows, distinctive black custom rims and paper dealer ads in place of license plates that fled the scene about 4:20 a.m.
In Southern California, the California Highway Patrol alerted officers in at least three counties to be on the lookout for the SUV.
Las Vegas Police Sgt. John Sheahan said the Range Rover was last seen near the Venetian resort as it headed north from the shooting scene on Las Vegas Boulevard.
Witnesses also told police the SUV and Maserati had come from the nearby CityCenter area, just south of the site of the attack.
"We have numerous witnesses to this," Sheahan said. "But what is the genesis of this? We don't know yet."
Predawn jogger Eric Lackey was on his way back to the New York-New York hotel when he snapped a cellphone photo of the blazing scene moments after the crash. Black smoke billowed from the flaming taxi, amid popping sounds from the fire.
Lackey, of Forest Hill, Md., said a security officer in a yellow shirt performed CPR on a person on the sidewalk while police officers canvassed a small crowd of perhaps 15 onlookers gathering at the scene.
"Police were asking if anyone was still in the vehicles and if they heard gunfire," Lackey told The Associated Press. "That's when I realized it wasn't just a regular accident."
Sheahan said police have video from traffic cameras at the intersection and were checking hotel surveillance systems. The video will not be made public, he said.
Police said the Maserati hit the taxi cab, which went up in flames, and the driver and passenger were killed. The male driver of the Maserati also died, and his passenger was shot.
The crumpled, gray sports car, which had no license plates, came to rest several feet away from the incinerated taxi.
"The people I feel sorry for are the people in the taxi," said Elvina Joyce, a tourist from Regina, Saskatchewan, Canada. "Seconds made all the difference in the world for them. Wrong place, wrong time."
Joyce and her husband, Dave Joyce, were among the guests staying in high-rise hotels around the scene who found police tape blocking access to normally busy pedestrian crossings at the intersection. Hotel security officers and police shooed away people with cameras, and footbridges linking resort hotels were closed. Traffic around the area was snarled.
Sheahan said the closures were expected to last most of the day while crime scene investigators collected evidence.
"CSI," said Dave Joyce. "There it is. Real crime scene investigators in Las Vegas."
A convention-goer, Jeff Martin, 33, of Columbus, Ohio, said he was unable to cross the Strip several hours after the attack.
"When you're out at 4 a.m. nothing good's going to happen," he said.
Sheahan said the attack was not a rolling gun battle as previously described. The SUV and Maserati were stopped or approaching a red light when at least one person in the Range Rover opened fire. Several people were inside the SUV, the sergeant said.
Six vehicles were involved in the crash that followed, including the taxi and Maserati. The taxi was affiliated with Desert Cab company, according to general manager Sandy Shaver. He declined to comment further.
The taxi might have been propane-powered, Sheahan said.
The incident marked the latest violence on the Strip since the beginning of the year. Two people were critically wounded in a shooting at a parking garage on Feb. 6, and a tourist was stabbed Saturday in an elevator at The Hotel at Mandalay Bay.
A spokesman for the Las Vegas Convention and Visitors Authority, Jeremy Handel, reassured people that much is being done to keep them safe.
"Recent incidents, while unfortunate, were isolated events," he said in a statement. "Las Vegas is among the safest travel destinations in the world and utilizes the most advanced technology and training to maintain a secure environment."
Las Vegas Police Officer Jose Hernandez acknowledged that the Strip has seen several violent incidents in recent weeks but said police have made arrests or identified suspects in each case.
"People don't have to worry," he said. "This is an unusual occurrence, as tragic as it may be."
The area near the scene of the latest shooting has been the site of high-profile violence in the past.
Rapper Tupac Shakur was killed in a drive-by in 1996 about a block away under similar circumstances, as assailants opened fire on his luxury sedan from a vehicle on Flamingo Road. The killing has never been solved.
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