The father of a six-year-old boy defended his son from a California mountain lion after the animal attacked and dragged him away.

The terrifying ordeal happened on 7 September, 2014, when the lion "came out of nowhere" on a trail at the Picchetti Ranch Open Space Preserve, near the Silicon Valley city of Cupertino.

The boy had been walking just metres in front of a group of parents and children when the lion pounced on him "like it would a deer" and hauled him along the ground.

Lt. Paul Foy of the California Department of Fish and Wildlife said the boy was targeted as the lion considered him to be the easiest prey.

"It's quite extraordinary the lion would attack a person with so many people in the immediate vicinity," said Foy.

The attack was thwarted when the boy's father and another man from the group shouted and acted aggressively toward the mountain lion, scaring it away.

"He's very, very lucky that the parents were so close," Foy added.

Authorities plan to deploy dogs to track the animal and will kill the lion "in the interest of public safety" if DNA samples from the lion's saliva on the boy's torn shirt match the captured animal.