Four people including the pilot have died and another person was critically injured when their hot air balloon crashed into the Arizona desert after eight skydivers had successfully jumped out of the basket.

The Kubicek BB 85 Z balloon went down on Sunday in Eloy, about 100 kilometres south-east of Phoenix, the US National Transportation Safety Board said on Monday (US time).

The cause remained under investigation.

“The balloon impacted desert terrain following an unspecified problem with its envelope,” the NTSB said, referring to the outer bag of the balloon.

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An initial inspection found no mechanical anomalies as both the balloon and basket appeared to be intact, the NTSB said, adding that the envelope would be inspected later. An electronic device containing flight information and a video camera have been sent to NTSB headquarters in Washington for further analysis, the NTSB said.

“It is important to clarify that the skydiving was intentional and was successfully completed by all skydivers before any issues with the hot air balloon were evident,” the Eloy Police Department said.

The company operating the flight, Droplyne Hot Air Balloon Rides, had a perfect safety record, according to its website.

Company representatives did not immediately respond to requests for comment.

Droplyne said it conducted daily flights that rise up to 3000 metres elevation from either the Eloy area of Arizona or Moab, Utah, depending on the time of year.

-AAP