The number of people unaccounted for after a deadly flash flood hit part of the Grand Canyon has fallen to one as US Park Rangers said they had managed to make contact with over a dozen people who had been missing.

A monsoonal downpour that lashed the northern side of the huge canyon sent torrents of water, rock and debris down a popular hiking course on Saturday, washing out campgrounds in Bright Angel Canyon and around the historic Phantom Ranch.

Two men are known to have died in the sudden flood whose bodies were recovered as search and rescue teams moved in, amid fears that many more could have been swept away at one of the most popular and dramatic tourist spots in the United States.

But late on Monday, Dave Black of the National Park Service said nearly all those who were known to be in the canyon had now been found.

"There is one person unaccounted for that we know of right now," he told reporters in Grand Canyon Village, Arizona.