Search and rescue operations underway following Grand Canyon flash floods

About 15 people are missing or unaccounted-for for after a flash flood in the Grand Canyon, the US National Park Service says.

The floods hit the Bright Angel Canyon and Phantom Ranch area on Saturday, local time, the service said, adding that it was working with Arizona authorities to evacuate people and account for missing individuals.

Torrents of water wiped out footbridges and significantly altered the landscape, widening the creek bed and creating what appeared to be a new river rapid.

Earlier, the park service said that more than 20 people were believed missing.

There were no confirmed deaths or injuries, the park service said in an email.

As of Sunday morning, local time, 62 people had been evacuated, and others were scheduled to be evacuated, it said.

As the park service tries to account for everyone in the area, it is asking anyone with details about people hiking or camping there to make contact.

It said it was working with the Arizona Department of Public Safety to continue evacuations on Sunday.

"This is a reminder of what a dynamic and active landscape Grand Canyon is," said Jack Schmidt, director of the Center for Colorado River Studies at Utah State University.

Popular tourist spots including the Bright Angel Campground, Phantom Ranch and parts of the North Kaibab trail remained closed while park officials surveyed the damage, the park service said.

More than 60 people were evacuated from Phantom Ranch, which has a historic canteen and dorms, and is a common spot for rafters to get off and on the river.

Erica Viola said she was at Bright Angel Campground when the rain started on Saturday afternoon, and she and about 50 other hikers watched the creek rise and then debris start to flow by, including what looked like a bunkhouse.

The group was taken by helicopter to safety, ending her adventure two days early, she said.

Parth Desai was hiking through a narrow passage in Bright Angel Canyon with a group of fellow physicians and a park ranger when the downpour started.

Later, as they made their way toward Phantom Ranch, a colleague shouted "Up, Up, Up, Up!" as a 1-meter debris wall headed toward them and they ran up into a patch of cacti, he said.

They were rescued by helicopter that evening after reaching the Phantom Ranch area, he said.

About 1 to 2.5 centimetres of rain fell within 30 minutes in the rocky area, where there is a steep drop in elevation, said National Weather Service meteorologist Justin Johndrow in Flagstaff.

"Most of it ran off instantly," Mr Johndrow said.

He said the flooding happened on the north side of the Grand Canyon, where Bright Angel Creek comes from the North Rim down to the Colorado River 1,828 meters.