A helicopter flying tourists to see the Hoover Dam crashed into a mountainside near Las Vegas, Nevada, killing four passengers and a pilot, a National Park Service spokesman said.

The Sundance Helicopters’ chopper was on a tour of Hoover Dam and heading back yesterday, NPS spokesman, Mr Andrew Munoz, said.

“It crashed in the River Mountains on the western side of Lake Mead National Recreation Area,” just before 5 pm, the spokesman added.

The cause of the crash was not immediately known.

“The area where the crash occurred is along the normal route helicopters take,” Mr Munoz said, noting that weather conditions were not unusual.

The Federal Aviation Administration was investigating.