(CNN) -- A helicopter that was taking passengers on a tour over Hoover Dam near Las Vegas crashed Wednesday evening, killing the pilot and all four passengers, a spokesman for the National Park Service said.
The crash occurred 4.5 miles west of Southern Nevada Water Authority in the Lake Mead Recreational Park, east of Las Vegas, said the spokesman, Andrew Munoz.
The Eurocopter AS350 helicopter crashed around 5 p.m. under unknown circumstances, Federal Aviation Administration spokesman Ian Gregor told CNN.
Sundance Helicopters said the aircraft was on a tour from the airport to the Hoover Dam and back. The company's website said it operated a fleet of 23 helicopters.
"All our helicopters are maintained with exacting precision and our pilots are trained and then retrained with ongoing recertification in excess of FAA requirements," it said.
CNN's Tina Burnside contributed to this story