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Four people have died and one person was critically injured after a hot air balloon crashed into the ground in Arizona on Sunday, authorities have said.

The incident occurred around 07:50 local time (14:50 GMT) in Eloy, a desert area roughly 65 miles (105km) south of Phoenix.

There were five people onboard when the balloon crashed, police said.

The cause of the incident is currently unknown.

The victims were identified by the Eloy Police Department on Monday afternoon.

The four who died were Chayton Wiescholek, 28, Kaitlynn Bartom, 28, Atahan Kiliccote, 24 and 37-year-old Cornelius Van Der Walt, identified as the pilot.

Valerie Stutterheim, 23, was injured and remains in critical condition, police said.

Jennifer Hubartt, Ms Bartom's mother, told a CNN affiliate early on Monday that her daughter "was a beautiful person".

"She recently became an RN and was making it on her own," she said.

Police in Eloy said they are investigating the incident in conjunction with the National Transportation Safety Board (NTSB) and the Federal Aviation Administration to determine the cause.

"Something catastrophic occurred with the balloon," local police told a CBS affiliate on Sunday.

When the hot air balloon initially took off on Sunday, there were 13 total adults onboard: a balloon operator, four passengers and eight sky divers, Eloy Mayor Micah Powell said at a press conference.

The crash occurred shortly after the skydivers completed their planned jump, Eloy Police Chief Byron Gwaltney said.

Investigators arrived at the scene shortly after the crash to examine the downed balloon, identified by the NTSB as a Cameron Balloons A160 aircraft, a NTSB spokesperson said.

The exact cause of the accident is still under investigation, the spokesperson said, but the NTSB identified that the balloon had an "unspecified problem with its envelope".

Mayor Powell said Eloy has a "very large skydive community" due to its large "drop zone" - an area where skydivers can land.

The craft will be brought to a secure facility for additional evaluation, officials said.

"While we continue our efforts, we ask for your thoughts and support for the families and loved ones affected during this difficult time," police said.