The pilot of the helicopter and all four passengers are confirmed dead, the Lake Mead National Recreational Area said on its Twitter feed.

The Eurocopter AS350 helicopter crashed during the late afternoon, according to Federal Aviation Administration spokesman Ian Gregor. The circumstances of the crash approximately 12 miles east of Las Vegas McCarran International Airport were not known, he said.

The crash occurred on the western side of the River Mountains about a half mile within the boundary of Lake Mead National Recreation Area and about 4 miles west of the Alfred Merritt Smith Water Treatment Plant, according to National Park Service spokesman Andrew Munoz.

The helicopter belonged to Sundance helicopters, according to the park service, and crashed near Lake Mead.

"Sundance Helicopters regrets to report that a Sundance helicopter with five people on board went down 16 miles east of Las Vegas at approximately 4:45 this evening," company CEO Larry Pietropaulo said in a statement.

"Emergency personnel on the scene reported there were no survivors. Names of the deceased are being withheld pending notification of the next of kin. Sundance Helicopters is cooperating fully with the FAA and the NTSB in the investigation."

Sundance offers a helicopter tour to the Hoover Dam from Las Vegas, according to the company's website.

The company told the FAA that the aircraft was theirs and was on an air tour flight from McCarran to the Hoover Dam and back, Gregor said.

Sundance was involved in another deadly air crash in 2003, when the pilot of a helicopter of the same model and all six passengers on board were killed when one of the rotor blades apparently struck the Grand Canyon wall in Arizona, according to a National Transportation Safety Board report of the incident.

Recovery operations have been suspended for the evening, Munoz said, and will resume on Thursday morning.

The FAA and the NTSB are investigating the crash, Gregor said.