A police helicopter and a water rescue unit were called to a search on the River Tay in Perth.
The alarm was raised at Tay Street at 1.25pm on Monday.
Police Scotland, the Scottish Fire and Rescue Service, mountain rescuers and the Scottish Ambulance were also at the scene.
Emergency service personnel were searching the water and adjacent Moncreiffe Island.
A police statement initially said officers were responding to reports of concern for a person.
However, the force later confirmed it was searching for missing woman Clare Marshall, 64.
A spokeswoman for the fire service said on Monday: “We received reports at 1.58pm on an incident on Tay Street.
“We have two appliances there as well as a water rescue appliance.
“We are assisting Police Scotland with this incident.”
One witness said: “I arrived on Tay Street at about 3.15pm.
“There was a helicopter flying quite low. There were also two fire engines as well as multiple police cars and an ambulance.
“A cordon was put up next to the steps up to the railway bridge.
“It appeared to be some sort of rescue. There was a large emergency presence.”
