Authorities are searching for a 14-year-old boy and a 62-year-old woman missing in Grand Canyon National Park after they were swept down a creek while crossing it in a remote part of the park.

Chief Ranger Matt Vandzura of the National Park Service says two fellow hikers alerted authorities by setting off an emergency GPS locator beacon in the backcountry area below the canyon's North Rim.

He says the two lost their footing and were swept away Saturday in Tapeats Creek, a tributary of the Colorado River.

Vandzura declined to identify the missing, the other hikers or their relationship to each other.

An investigation is underway but authorities have not concluded how the two were swept away.

A helicopter and a drone on Monday were assisting searchers on the ground.