MASON CITY, Iowa (AP) -

Authorities have identified two of three people who were killed when a medical helicopter crashed into a northern Iowa field.

Witnesses told deputies that the helicopter burst into flames when it went down around 9 p.m. Wednesday just north of Ventura in Cerro Gordo County. The aircraft was affiliated with Mercy Medical Center-North Iowa and had been headed to Emmetsburg to pick up a patient.

The hospital identified two of the victims: nurse Shelly Lair-Langenbau and paramedic Russell Piehl.

The pilot was not identified. The helicopter was operated by a Lewisville, Texas-based service company, Med-Trans Air Medical Transport. Company officials didn't immediately return messages left Thursday by The Associated Press.

Sheriff Kevin Pals says the crash cause is being investigated.

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Three people are dead after a medical helicopter flying out of Mason City, Iowa, crashed into a field, authorities say.

Cerro Gordo County Sheriff's Department Lt. Matt Klunder said the helicopter was affiliated with Mercy Medical Center and that a pilot and two nurses were killed.

Klunder said the crash occurred about 9 p.m. Wednesday near Ventura, Iowa.

The identities of the victims were not released, and the cause of the crash was under investigation.