ACT Work Safety Commissioner Mark McCabe, who met representatives of about 41 businesses from the eastern half of the historic building on Wednesday, said it was highly unlikely they would be able to open before next week. He estimated that about a third of the businesses in the row had been severely damaged, while about a third were minimally affected.

Engineers Advanced Structural Designs on Wednesday confirmed an urgent public-safety hazard - loose and damaged roof tiles that Mr McCabe said could fall to the street in the wind. Work began to remove up to half the historic ceramic tiles, and workers are trying to salvage as many as possible.

Mr McCabe hoped the work would finish on Thursday, allowing East Row to be reopened to buses and the exclusion zone to be brought back to the footpath.

But the laneway behind the damaged building remains closed, which is a sticking point for many of the businesses, including nightclubs keen to reopen before the weekend.

Mr McCabe said businesses must have two fire exits to reopen, and given that the second exit of some leads into the laneway, they could not open until the exclusion zone was shifted.

Structural engineers were also checking the extent of damage if other parts of the building had escaped structural damage. If so, those businesses would need to ensure they had gas, water and electricity supplies, airconditioning and fire exits before they could

reopen, said Mr McCabe, who would be surprised if any opened before the weekend.

Meanwhile, Mr McCabe acknowledged the frustration of business owners who had been locked out but said safety must come first. ''We will do everything to get them back in as quickly as possible,'' he said. ''I don't want to put bureaucratic obstacles in their way, but we've got to do it right.''

Workers on Wednesday tried to stabilise the kitchen at Coo - where the fire was believed to have started - so investigators could enter. Mr McCabe said the fire had burnt into the floor above the restaurant and the tin roof above that, preventing investigators from getting in. But he expected them to be able to enter by Thursday.

Mr McCabe was still trying to establish who owns the Sydney Building, because of multiple title owners and no definitive list.

The ACT and Region Chamber of Commerce and Industry will hold a forum for business owners at 11am on Friday in East Row at which they will have a chance to question government representatives.

Chamber chief executive Andrew Blyth said business owners were concerned about uncertainty over repairs, traffic and parking issues, and financial support.