Phoenix Fire Department crews searched a mile up and down a dangerous portion of the Salt River for two men who reportedly yelled for help and then went missing Sunday morning.

By mid-afternoon, the fire department turned over the scene to the Phoenix Police Department. There was no sign of the two men as of just before 4 p.m. PST.

Initial reports from witnesses said the men may have been on a kayak, paddle board or boogie board, but those details were uncertain, fire department spokesperson Scott Douglas said in an emailed statement.

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Arizona’s Phoenix Fire Department unsuccessfully searched for two men who went missing in a hazardous portion of Salt River Sunday. 

ABC15 Arizona reported that a person ran for help and came back, but by then, two men were out of sight.

Multiple search parties deployed without success, the city’s fire department said in a statement. The disappearance happened in a portion of the river considered "dangerous" and closed for recreation, according to the department.

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"We urge all people to remain out of the water due to the potential life safety hazard that this swift water presents," Douglas said in a statement.

The city's police department turned over all inquiries to the fire department.