Thirteen people were aboard a hot air balloon flying over Eloy, Arizona on Sunday when the craft crashed, ABC News reports.
The passengers included eight skydivers, four passengers, and the balloon pilot, according to police.
All of the skydivers managed to exit the balloon safely. They dove before "any issues with the hot air balloon were evidence," according to police.
The crash occurred at approximately 7:50am in the desert outside Eloy, approximately 65 miles south of Phoenix.
The passengers who were killed in the crash were Chayton Wiescholek, 28, of Michigan; Kaitlynn Bartom, 28, of Indiana; and Atahan Kiliccote, 24, of California, police said.
Cornelius Van Der Walt, 37, who piloted the balloon, was also killed in the crash.
One of the victims died at the scene, according to Fox10 Phoenix. Three others survived the impact but later died from their injuries at Casa Grande Hospital.
The youngest individual left onboard, Valerie Sutterheim, 23, of Arizona, survived the crash but was in critical condition.
"The Eloy Police Department extends its deepest condolences to the families and friends of those involved in this heartbreaking incident," the department said in a statement.
The National Transportation Safety Board has launched an investigation into the crash, and said in a preliminary report that the balloon suffered an "unspecified problem with its envelope."
"Investigators have not found any mechanical anomalies with the balloon during their examination. They have also separated the balloon from the basket, and everything appears to be intact," the NTSB said on Monday. "Later today, they will be examining the envelope for any anomalies. An electronic device that could have relevant flight information and a video camera have been sent to NTSB headquarters in Washington, D.C., for further analysis."
The NTSB will continue to interview witnesses.
The balloon reportedly was gaining and losing altitude rapidly just before the crash, according to witnesses who spoke to Phoenix broadcaster KNXV.