At least three people were killed and four others injured Saturday when a helicopter carrying tourists in Arizona went down in the Grand Canyon, authorities said.

The accident took place at around 5:20 pm in Grand Canyon West, located in northwestern Arizona, said Hualapai Nation police chief Francis Bradley.

Local media reported the Eurocopter EC130 helicopter, whose operator was unknown, was traveling on a tour.

“The investigation is ongoing,” Bradley told AFP, noting that there was no information immediately available on the circumstances surrounding the tragedy.Allen Kenitzer, of the Federal Aviation Authority’s Office of Communications, told AFP the aircraft sustained “substantial damage.”

The FAA and the National Transportation Safety Board will investigate the crash, he added.