A small medical transport plane crashed and caught fire Tuesday on the Navajo Nation in northern Arizona, killing four people, the tribe said in a statement.

A Beechcraft 300 from the CSI Aviation company left Albuquerque, New Mexico, with four medical personnel on board, according to the Federal Aviation Administration and other agencies. It crashed in the early afternoon near the airport in Chinle, about 300 miles (483 kilometers) northeast of Phoenix.

“They were trying to land there and unfortunately something went wrong,” district Police Commander Emmett Yazzie said.

The crew was planning pick up a patient who needed critical care from the federal Indian Health Service hospital in Chinle, said Sharen Sandoval, director of the Navajo Department of Emergency Management. She said the plan was to return to Albuquerque. The patient’s location and condition were not known Tuesday evening.

Tribal authorities began receiving reports at 12:44 p.m. of black smoke at the airport, Sandoval said. The cause of the crash wasn’t known, the tribe said. The National Transportation Safety Board and the FAA are investigating.

Navajo Nation President Buu Nygren said in a social media post that he was heartbroken to learn of the crash.

“These were people who dedicated their lives to saving others, and their loss is felt deeply across the Navajo Nation,” he said.

Medical transports by air from the Navajo Nation are common because most hospitals are small and do not offer advanced or trauma care. The Chinle airport is one of a handful of airports that the tribe owns and operates on the vast 27,000 square-mile (70,000 square-kilometer) reservation that stretches into Arizona, New Mexico and Utah — the largest land base of any Native American tribe.

In January, a medical transport plane crashed in Philadelphia, killing eight people. The National Transportation Safety Board, which is investigating the crash, has said the voice recorder on that plane was not working.

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Associated Press journalists Hannah Schoenbaum in Salt Lake City and Felicia Fonseca in Flagstaff, Arizona, contributed to this report.