BARRIE, ONT. -- Eleven people were injured, including four in critical condition, when a fire broke out at an apartment building in Bradford West Gwillimbury Monday afternoon.

Thick, black smoke poured out of the fifth-floor Holland Street West tower near Simcoe Road around 2 p.m. as fire crews rescued multiple people from balconies.

Bradford West Gwillimbury Fire Chief Jim Kay said close to 100 people inside the 84-unit building were evacuated.

"Many people had left on their own. They heard the alarm bells," he said. "We still have a number of pets in the building that we are going to remove and reunite with their owners."

The fire chief said the damage appears to be contained to the 5th and 6th floors. He noted that those tenants could be displaced for some time.

Hours after the blaze started, fire crews were going floor by floor to check the air quality.

Kay said no one would be permitted back inside the highrise until a structural engineer could determine if it was safe to do so.

The town set up an evacuation centre at the Danube Seniors Centre for displaced tenants of the apartment building. It said beds would be available for anyone needing overnight accommodations.

The Ontario Fire Marshal's office has been called to investigate the cause of the blaze. However, Kay said that investigation wouldn't likely start until the building's integrity is ascertained.