City officials say a section of downtown St. John's will remain closed to traffic until at least noon on Friday following a fire that destroyed three buildings on Wednesday.

The city said the closure affects Duckworth Street, from McBride's Hill to New Gower Street, and Bate's Hill.

Fire investigators have been combing through the rubble of three adjoining buildings on that section of Duckworth Street for clues as to what sparked the blaze.

The buildings housed businesses including Food for Thought, the provincial office of Oxfam Canada, as well as other offices and apartments.

The closure of the street also affected other businesses in the immediate area.

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Brian Vallis has been forced to keep his pizzeria closed since the fire. (CBC)

Brian Vallis, the owner of Piatto Pizzeria and Enoteca, had to close his restaurant on Wednesday while firefighters battled the blaze directly across the street.

Vallis said he watched nervously from his century-old building as the fire raged.

"If that wind had changed direction and started coming over this way, with the sparks and the debris, we could have been the next building on fire."

Vallis had high praise for the work of emergency responders and investigators, and he has been showing his appreciation by giving free pizza to anyone working at the scene.

Meanwhile, Oxfam's Bill Hynd watched from across the street as crews moved through the wreckage of his former office.

"It looks like it will never be safe to enter," said Hynd. 

Oxfam lost decades of documents, reports, videos and other materials. And while an archivist has offered to assist with salvaging some of those materials, Hynd was pessimistic about what could be saved.

"I don't think we'll ever be able to enter that building again," Hynd said. "That makes it overwhelming."

Red Cross, community helping

On Thursday, the Red Cross was helping two tenants who lost their homes in the fire.

Two men received food and clothes, and one of them was put up in a motel.

A spokesperson said two other tenants were out of town, and have had no contact with the Red Cross.

Meanwhile, plans were coming together for a fundraising concert.

"We thought even [it would be worthwhile] if we only gave them a little bit of money toward covering temporary rent," said Angela Record, co-organizer of Community Cares, a benefit set for the Rockhouse bar on George Street on Sept. 15.

Funds raised will go to the tenants of three residences, as well as Oxfam and other businesses affected by the fire.

"They're really worthy organizations, and we all know how much good they do in the community," said Record.

"It's just heartbreaking that these people are now without premises."