The popular Taste of Carnival was set to be held in Preston's Flag Market with performances from DJ Toro, Abelwell, Mento P and Steel Pans due to take place.
In a statement published online Preston City Council said: "Lancaster Road will open allowing left hand turn only for traffic on to Church Street. A cordon will be in place spanning across Church Street between Baluga Bar & Co-Op bank and from corner of Cheapside to former Fishers bar.
"Baluga Bar, Slug & Lettuce and the businesses on Lancaster Road will now fall outside the new cordon as will Waterstones bookshop. Syke Street and Avenham Street will remain closed to allow the emergency demolition works to take place. Vehicle access to Cheapside and the area around Preston Market is still restricted.
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"There are vehicles that need to be relocated, so the road openings described above will be released when safe to do so in the next two hours. Emergency services & Local Authority Building Control officers will remain in the area over the weekend."
Adrian Phillips, Chief Executive, said: "Everyone is concerned about the devastating effects recent fires have had on Preston city centre.
"We understand the impact road closures and restricted access is having on city centre businesses, and as such this is being closely monitored and regularly reviewed. Access will be allowed as soon as it is safe to do so, and further updates will be provided by the relevant agencies."
Emergency demolition work is required at the site over the coming days with completion expected by Monday, May 23.
It is expected that roads at the front and rear of Church St and Syke Street will be closed until Monday afternoon.
The fire ripped through the Church Street building on Thursday night with firefighters spending several hours bringing the blaze under control.
Lancashire Police have confirmed that a 14-year-old boy has been arrested in connection with a joint investigation with Lancashire Fire and Rescue Service.