A cougar attack that injured an 18-month-old boy in a British Columbia park was stopped after the child's grandfather and a family friend scared off the animal, which also lunged towards the boy's four-year-old sister, parks officials said Tuesday.

The boy was listed in serious condition in Vancouver's Children's Hospital after he was attacked Monday evening in Kennedy Lake Provincial Park. The attack happened a popular day-use spot at Kennedy Lake, east of Ucluelet.

Bob Hansen, who works for the park and specializes in incidents involving wildlife and people, said the group had packed up for the day and was heading up a trail to their car when the attack occurred.

Hansen said the tot, his four-year-old sister, their grandfather and a friend of the family were together when the cougar emerged from the forest.

The boy was walking about three metres in front of the group, said Hansen.

"From what I understand, they yelled and screamed and the cat dropped the child," said Hansen. "So it sort of bit the child and ran towards the four-year-old, but didn't hit the four-year-old."

Hansen said the cougar didn't leave the area right away, so the adults attempted to scare it off before they returned to their vehicle.

Renee Wissink, manager of resource conservation at the park, said the child's father asked for help at a visitor's information centre located just minutes away down the highway and an ambulance was called.

The boy was eventually transferred to Vancouver.

The Kennedy Lake day-use area was closed to the public as wildlife officials searched for the cat.

Hansen said two teams of park staff and conservation officers and two teams of hounds were searching for the cougar.

"If need be we'll keep going 24 hours a day until this cat is located," he said, noting park officials are reassessing the situation every four to six hours.

In a statement released by the Provincial Health Services Authority, the family thanked everyone who has helped out, as well as their friends on the west coast of Vancouver Island.

"The family is focusing all of their energy on their son's recovery and are asking the media to please respect their privacy today and in the days ahead so they can concentrate on their son's health," said the statement.

Community members reacted quickly and wished the family well on several Facebook pages.

"If that cougar was on my island, I would be pit lamping it right now," wrote Lana Gibson, a long-time resident of nearby Tofino. Pit lamping is a procedure in which hunters use lights to help kill prey at night.

"I do amazingly well with a Ruger 22," wrote Erika Scott, referring to a firearm.

"Any cat that attacks a kid should be a dead cat," added Dave LeBlanc. "The excuse that humans encroach on cougar habitat is wrong. People have been safely going to Kennedy Lake for decades."

A wolf and cougar advisory has been in effect in the region since Aug. 13 because of increased activity in the area.

Wissink said a cougar approached a jogger on a local road on Aug. 1, and about a week later, a cougar was destroyed in Ucluelet.

Ucluelet Mayor Eric Russcher said he heard sirens Monday night but by Tuesday morning he was still trying to confirm whether or not the child was a resident of Ucluelet.

Russcher said cougar attacks are rare.

In August 2006, a cougar attacked a four-and-a-half-year-old boy who was camping with his family at Schoen Lake Provincial Park, about an hour north of Campbell River.

The boy survived the attack, suffering bite wounds to his head and scratches to his upper body.

Just months earlier, six-year-old Bryce Forbes received a bravery award for saving his little brother from a cougar in Gold River, a community located about 355 kilometres north of Victoria.