The serious injuries actor Jeremy Renner suffered while using a snow tractor to free a snowbound motorist on a private mountain road near Lake Tahoe appear to be the result of a “tragic accident,” the sheriff in Reno said Tuesday.

Renner was “run over” by an “extremely large piece of snow-removal equipment” weighing “at least 14,3330 pounds,” according to local authorities.

The 51-year-old “Avengers” star was seriously hurt when he was run over by his own snowcat after using it to free a vehicle driven by a family member that became stuck in 3 feet of fresh mountain snow on New Year’s Day, Washoe County Sheriff Darin Balaam said.

“At this point in the investigation … we believe this is a tragic accident,” the sheriff said. “He was being a great neighbor and he was plowing those roads for his neighbors.”

The accident left Renner in critical but stable condition with chest and orthopedic injuries, according to a publicist and sheriff’s officials who said Renner was flown by medical helicopter about 25 miles to a Reno hospital.

Washoe County Sheriff Darin Balaam said during a press conference Tuesday that the actor’s PistenBully was “stuck” when the star attempted to “retrieve” the snowcat and “get (it) moving.”

Although the 51-year-old was “successful,” he was off of the machinery and “speaking to a family member” when the PistenBully subsequently “started to roll.”

The sheriff explained, “In an effort to stop the rolling PistenBully, Mr. Renner attempted to get back into the driver’s seat of the PistenBully. Based on our investigation, it’s at this point that Mr. Renner (was) run over.”

Renner posted an Instagram photo of himself in a hospital bed and a message.

“Thank you all for your kind words,” it said. “Im too messed up now to type. But I send love to you all.”

“He was helping someone stranded in the snow,” Reno Mayor Hillary Schieve told the Reno Gazette-Journal Monday night. She said she and the actor are friends and that she was called about the accident shortly after it happened near the Mt. Rose Highway that connects Reno to Lake Tahoe.

“He is always helping others,” the mayor told the newspaper.

The Associated Press contributed to this report.