Twenty people were displaced when a fire at a vacant building in Hartford spread to a multi-family building on Thursday night.

Firefighters responded to a blaze at an unoccupied building on Ward Street around 11:45 p.m. and found that the three-story structure was fully engulfed in flames, according to the Hartford Fire Department.

The fire was so intense the structure collapsed and spread to another three-story building occupied by multiple families, fire officials said. Everyone inside made it out safely.

The fire was put out but not before the vacant building and the multi-family structure sustained heavy damage. As a result, 20 people were left without a home, officials said. This included 18 adults and two children.

The fire department's Special Services Unit and the American Red Cross responded to assist the displaced residents.

The cause of the fire remains under investigation.