A California family’s idyllic Labor Day picnic turned into a nightmare when their young son was attacked by a mountain lion — only to be rescued when his dad fought off the big cat.

The heart-pounding encounter took place just before 4:30 p.m. Sunday, as the boy’s family was relaxing at the Tapia Day Use Area of the Malibu State Creek Park in Calabasas, the Los Angeles County Sheriff’s Office said.

At least six adults and several children were at the picnic when a mountain lion grabbed the 5-year-old boy by the head and started to run, KTLA5 reported.

“Somebody screamed the baby’s name, and his dad started running,” the victim’s aunt told the outlet.

“The father grabbed the mountain lion with his hands, and he just fought. Then the mountain lion let go.”

About 40 onlookers watched the terrifying encounter — with some telling KTLA that the mountain lion looked completely unafraid during the attack.

Male mountain lions can weigh up to 150 pounds and be up to 8 feet long.

The boy was airlifted to Northridge Hospital Medical Center for non-life-threatening injuries, according to the California Department of Fish and Wildlife.

He was released late Sunday, but returned to the hospital Monday due to complications with injuries to his eyes, KTLA said.

When California State Park rangers and CDFW officers responded to the scene of the attack, the mountain lion was crouched up in a tree near a picnic area.

The animal was deemed a threat to public safety, and was euthanized by a ranger, the CDFW said.

Wildlife officers also collected evidence of the attack from the boy’s injury, including DNA swabs from the bite marks that were matched to the mountain lion.

“CDFW and State Park officials are thankful that the family is safe, and the child is recovering and no one else was injured,” the CDFW said in a statement.