Two young sisters were burned after two vans parked side by side caught fire outside a Fridley Walmart on Tuesday morning in a suspected case of negligence, authorities said.

A 6-year-old girl suffered critical burns that Fridley Police Lt. Jim Mork described as life-threatening. Her 9-year-old sister was less seriously burned, Mork said. Both were taken by ambulance from the store in the 8400 block of NE. University Avenue to HCMC.

The younger girl was burned over most of her body and was “not very alert,” an emergency responder was heard saying over dispatch audio. The other girl had burns to her hands, arms and face, and was described as alert, the audio disclosed.

The girls were alone in the van for 45 minutes to an hour as their mother shopped in the store, Mork said.

Later Tuesday, the Anoka County Sheriff’s Office announced the arrest of a 70-year-old man on suspicion that his extreme negligence was behind the fire that engulfed the van next to the one occupied by the children. Inside the torched van was the man’s wife, who escaped unharmed, said Sheriff’s Lt. Daniel Douglas.

“I can’t provide many details,” Douglas said, “but we are not calling it arson; simply negligent fires.”

The man remains jailed without bail and has yet to be charged. The Star Tribune generally does not identify suspects before they are charged.

Mork said the girls might have been sleeping at the time and added that leaving children that young alone in a vehicle is not against the law.

The van occupied by the children is part of a fleet owned by Universal Transit Services, based in Champlin. Company owner Emiru Hika identified the girls’ mother as Essie McKenzie, of Coon Rapids. Hika said McKenzie was a driver for him until July 25 and was not supposed to be using the van.

“She was hysterical,” Mork said of the mother. “Our officers tried to comfort her, and chaplain from a local church also arrived on scene to provide comfort.”

Authorities were contacted about one of the vans catching fire shortly before 7:15 a.m. A woman got out of the van, and flames from that vehicle ignited the van to its left where the children were, Douglas said. A car to the right of the two vans also was slightly damaged by the flames.

Witness Pamela Jacobson saw the woman trying to reach into the first van, which had North Carolina license plates, for her purse as the burning vehicle sent dark smoke skyward. She then saw the flames leap from one van to the other.

“Get out of there!” Jacobson recalled yelling to the woman, along with others. She then heard someone say that kids were in the van.

The next thing she knew, emergency medical responders “had them laying on the ground. I don’t know how they got them out of the van. Things were happening so fast. People were running everywhere. It was craziness.”