Calls and emails to Nevada-based Papillion for comment on the crash were not immediately returned on Sunday.
Bradley of the Hualapai Nation Police Department also wrote in a statement that the accident occurred at around 5:20 p.m. local time near Quartermaster Canyon. There were a total of seven people on board, including the pilot.
A Federal Aviation Administration spokesman, Allen Kenitzer, told The A.P. that the Eurocopter EC130 crashed in unknown circumstances and sustained heavy damage.
Bradley said first responders are at the scene with the four injured people, but strong winds gusting up to 50 miles per hour and rugged terrain were making it hard for crews to reach them.
Images emerged on Twitter of flames and thick black smoke rising from among the layers of rock at the scene of the crash.
The FAA and the National Transportation Safety Board will investigate, Kenitzer said.
The company's website said it flies roughly 600,000 passengers a year around the Grand Canyon and on other tours.
"This is not just the fact that a helicopter crashed, this is a human tragedy". The pilot and five passengers were killed; one passenger survived, NTSB report shows. The cause of the crash is now unknown.