Pc Nick Downing was on duty in the city's Albert Square when the heart-warming moment was captured in an image which has now been shared on social media.
The Durham Police officer, who was sent to Manchester on Wednesday, said: "Throughout the day the people and businesses of Manchester were extremely supportive - I can't recall in the past 14 years such an outpouring of appreciation by the public.
"I shook so many hands and was photographed more than on my own wedding day - the Manchester public were amazing.
"I left Manchester that evening, a couple of hours after the vigil at Albert Square had finished, and made my way back to County Durham arriving home at around midnight.
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"It was a long but rewarding shift.
"I am proud to have been able to support the people of Manchester, but I know if I hadn't taken that call there are many other officers who would have done just the same.
"I would like to say that although I played a small part, there are many other officers who worked longer hours, in more challenging situations, all of whom have my utmost respect."
The black and white photo was taken by Natalie Thornley.