Hualapai Nation Police Chief Francis Bradley Sr said the pilot had a severe limb injury and another of the passengers suffered severe burns.
Images have emerged showing flames and thick smoke rising from the boulder-strewn crash site.
Authorities said all four were level 1 trauma patients. Updates on their conditions were not available.
Douglass said the helicopter plummeted after circling twice, as if the pilot was searching for a spot to set the aircraft down.
He said the helicopter was on a tour.
Teddy Fujimoto was in the area taking photographs when he heard an explosion, according to CNN. The ladies were screaming.
Losing his sons felt like a "light had gone out", he said.
Jason Hill, a corporate senior associate in the firm's office in Milton Keynes, England, died in the crash along with his younger brother, 30-year-old Stuart, and Stuart's girlfriend, 27-year-old Becky Dobson. The pilot and three other British tourists survived.
A similar situation occurred on July 3 of the same year when an Airbus AS350 B3e helicopter collided with a parked vehicle in Frisco, Colorado, and "was destroyed by impact forces and a postcrash fire", the report states.
The aircraft sustained substantial damage as a result of the crash.
Bradley, the police chief, said a storm had passed through the area around the time of the early-evening crash, but declined to speculate on whether it was a contributing factor.
Papillon Airways says on its website that it is "the world's largest aerial sightseeing company" and that it provides "the only way to tour the Grand Canyon". They were with a group of friends to celebrate Stuart Hill's birthday in Las Vegas and took the Grand Canyon sightseeing tour on tribal land.
The company says it flies around 600,000 passengers a year over the Grand Canyon and on other tours.
As 9Wants to Know has outlined since a 2015 Flight for Life crash in Frisco, Colorado, most helicopters in use today have fuel systems that remain vulnerable to rupturing after otherwise survivable crashes. It will then be liable for your safety, and should ensure that the local company it has booked you with is properly licensed and professionally operated.
While emergency workers and the volunteers with medical training worked, other bystanders would come down to see what they could do, Kineally said.