(NewsNation) — A hot air balloon crashed Sunday morning, killing four people on board and critically injuring one in Elroy, Arizona, according to the Elroy Police Department.

The National Transportation Safety Board and the Federal Aviation Administration have launched an investigation into the incident, but the initial cause of the crash remains unknown.

The department has not yet released the names of the four victims, but family and friends identified to of the victims as 28-year-old Katie Bartrom and hot air balloon pilot Cornelius van der Walt to ABC 15.

One person was pronounced dead on the scene and the other three deceased died at the hospital, the report said.

The hot air balloon was carrying 13 people — eight skydivers, four passengers and a pilot — before it crashed, Elroy Mayor Micah Powell said. The eight skydivers had exited the gondola before the balloon fell, making a hard impact, according to the report.

Powell said a witness claimed the balloon was deflated and plummeted straight down, the New York Times reported.

Bartrom’s mother, Jennifer Hubartt, told ABC 15 that her daughter was an adventurer who loved to skydive.

“It’s kind of somber here at home. We’re crying about her on and off and talking about her on and off still trying to make it real. She was a beautiful person, she recently became an RN and was making it on her own,” Hubartt said.