A search is under way for an 11-year-old Calgary boy who fell into the Yoho River and was swept away, according to Parks Canada officials.

Two boys fell into the river at about 7:40 p.m. on Friday near the Takakkaw Falls Day Use Area in Yoho National Park, said Parks Canada spokeswoman Tania Peters.

The boys were with their family on the river bank, but Peters says there are very few details as to how the fall happened.

"What I do know is that they were on the banks of the Yoho River and two boys actually slipped and fell in," Tania Peters told CBC News.

"One was immediately pulled out, and despite great efforts by people in the vicinity to pull out the second boy, they were unsuccessful and he was swept downstream," Peters said.

Parks Canada led an extensive aerial and ground search of the Yoho River until 10:30 p.m., supported by local emergency services and two helicopters.

The search operation resumed at first light on Saturday, with a search dog being brought in as well.

"The thoughts of all Parks Canada personnel are with the young man's family and friends," said Peters.

The Takakkaw Falls parking lot is located next to the Trans-Canada Highway, just east of Field, B.C.

Earlier this month, a 21-year-old man from Calgary died while hiking in Yoho National Park.

RCMP said the man was with a group of friends in the alpine above the Little Yoho Campground when he lost his footing and fell 200m to his death.

And last year, 19-year-old Jeremy Prendergast from Calgary fell to his death in the 100-metre high Twin Falls, about eight-kilometres from the Takakkaw Falls parking lot.