An aircraft operated by Sundance Helicopters crashed into a mountainside near Lake Mead shortly before 5 p.m. on Wednesday, killing the pilot and four passengers. Their identities haven't been released.

According to The Associated Press, teams of recovery and investigative personnel are heading to the crash site.

Authorities said the helicopter crashed during a tour of Las Vegas and the Hoover Dam.

National Park Service spokesman Andrew Munoz told the media that the helicopter crashed into the River Mountains surrounding Lake Mead. He added that numerous people heard the crash and reported that they saw smoke some four miles west of the edge of the lake.

When a search and rescue team from the Las Vegas police reached the site, Munoz said they confirmed that all five on board were killed.

According to The AP report, the crash site isn't accessible by road, which slowed down the initial recovery efforts and forced officials to delay the rescue and recovery until Thursday.

A spokesman for Sundance Helicopters told The AP that the helicopter was giving a local tour when it went missing.

Ian Gregor, a spokesman for Federal Aviation Administration, told The AP that the helicopter was an AS-350 that can hold up to six passengers. The federal agency's records show that the helicopter was built in 1989, according to The AP report.

It is still unclear what might have caused the crash, as Munoz told the media that there were no notable conditions that might have caused the accident.