One person has died and 15 remain missing or unaccounted for after flash flooding swept through parts of the Grand Canyon, the National Park Service (NPS) has said.

The flood hit Bright Angel Canyon and the Phantom Ranch area on Saturday afternoon, wiping out footbridges and propelling boulders downstream.

The body of a 46-year-old man was found on Sunday evening near Crystal Rapids along the Colorado River, the park service told CBS News, the BBC's US partner. Sixty-two people have so far been airlifted out of the area.

"The whole thing was terrifying," said Nikki Baggs, 41, who was among those to be airlifted out of the bottom of the Grand Canyon with her two friends.

"It was a beautiful day and then people were screaming, running," she told the BBC.

Baggs said she and her friends had just dropped off their belongings at a cabin in Phantom Ranch - a remote lodge at the bottom of the Grand Canyon - when they decided to venture out to enjoy the nice day. Before they knew it, a flood of water was sweeping through the area.

As soon as the rain hit, Baggs and her friends headed toward higher ground, where they sat at a picnic table, before rangers yelled to them to run again to a different ledge, where they waited with others for hours before they were evacuated at around 21:30 local time (04:30 GMT).

Baggs said she and her two friends had been looking forward to a steak dinner at Phantom Ranch - but were now just grateful to be alive thanks to a swift response from park rangers.

"It was a really uniquely co-ordinated effort," she said. "That's what made us feel safe about all of it in an unsafe situation."

Baggs said she and her friends watched from higher ground as bridges were swept away.

The recent rains in the Grand Canyon area, and more widely in south-western parts of the US, are due to monsoonal showers.

A change in wind direction at this time of year pulls warm, moist air northward from the Gulf of California and the tropical Pacific, triggering storms over mountainous terrain.

The storms are difficult to pinpoint in forecasts and so can strike without warning. But because the ground is usually very dry, any heavy downpours lead to dangerous flash flooding and frequent lightning which increases the threat of wildfires.

Flood watches from the National Weather Service cover large parts of Arizona, as well as New Mexico, Utah and Colorado. There are lots of showers currently showing on the weather radar and these downpours will continue during Monday.

The threat of flooding is something that will remain for many more weeks. The North American monsoon season usually runs to the end of September.

The NPS said it was looking for information about 15 people who were thought to be missing or unaccounted for.

It reported that flooding had caused significant damage in some areas and that trails in the area have been closed.

Overnight guest lodgings in the South Rim will be stopped from Monday until further notice as the floods have caused "extensive damage" to the national park's water infrastructure.

The NPS asked anyone who knew of hikers or backpackers who were in the inner canyon along the Bright Angel Creek corridor on Saturday to get in touch.

The NPS also warned that more thunderstorms and heavy rainfall were forecast for Sunday and Monday, which could lead to "additional flash flooding, debris flows, rockfall and changing trail and river conditions".

The Grand Canyon is one of the most popular national parks in the US, with about five million people visiting each year. The Bright Angel trail is its most popular hike.