DUP man Brian Kingston was speaking after a book of condolence was opened in Belfast City Hall at 11.30am – little more than 12 hours of the explosion at Manchester Arena.
In addition, the building itself will tonight light up in the colours of the Union Flag in a sign of solidarity.
The book was opened by the city’s Sinn Fein Deputy Lord Mayor Mary Ellen Campbell, because the lord mayor himself was in London attending a garden party at Buckingham Palace.
Speaking to the News Letter, Mr Kingston said that he had studied physics at the University of Manchester, and regarded the city as his “second home”.
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“Manchester has suffered before from terrorism, and of course Belfast knows so much about the devastating impact of terrorism,” he said.
“We must stand resolute: that they must not win.”
Councillors from the UUP, TUV, Alliance, SDLP, PUP and Sinn Fein were all among the first flush of people paying tribute to the victims of the blast and to the bereaved from 11.30am onwards, and council CEO Suzanne Wylie also extended “heartfelt sympathy” to those people affected.
Michelle O’Neill, Sinn Fein’s leader in Northern Ireland, also added her name to the book later in the day.
In the past year or so, the council had also opened books of condolence after the Nice attack, the Westminster bridge attack, and the death of Martin McGuinness.
Husband and wife Ann and David Irwin, both 69 and from Crawfordsburn in Co Down, were among the first non-political figures to arrive at city hall for the signing.
Mrs Irwin said she knew some people living in Manchester, including one person who worked in a hospital there.
The self-catering business owner voiced “gratitude to all of the people like the ambulance and police” for the work they had done in the bomb’s aftermath.
“I’m sure they thought everything like this was over,” she said.
“There’s nowhere safe in the world nowadays. We just have to go out and hope.”
Also leaving a message was Mary Lennox, 41 and from east Belfast.
“I just couldn’t believe it – I was in total shock,” she said of the moment she heard the news.
“I [wrote] that I’m awful sorry, and that I feel for the families over there. I’ve been thinking about them.
“It’s ridiculous what’s went on over there.”
The book is available to sign from 8.30am to 5pm Monday to Friday.
It is also open from 10am to 4pm on Saturday and Sunday.
However, today and tomorrow (Tuesday and Wednesday) access to the hall is by the rear entrance only. The front entrance will reopen on Thursday.