Fire investigators are looking into the cause of a fire that sent two people running for safety and left their Northwest Side home heavily damaged.

Firefighters found flames shooting through the roof of the home in the 5500 block of Southwick Street when they arrived shortly after midnight Thursday. 

It took them about 20 minutes to put out the flames, fire officials said. Two people who had been inside had already escaped safely. 

Firefighters said it appeared the fire started in a garage area and spread to the home, causing heavy damage. At last word, investigators had not determined the cause of the fire.