FORT WORTH - A vacant warehouse just outside downtown was destroyed by fire early Saturday morning.

Firefighters responded to the massive blaze at the commercial structure in the 700 block of North Main Street shortly before 5:30 a.m., according to the Fort Worth Fire Department.

Upon arrival, crews found heavy fire showing from the first and second floors of the vacant structure, fire officials said.

"Firefighters know these buildings well -- having fought a second alarm fire in the same building not even two weeks ago, so operations went defensive almost immediately," the department said in a social media post.

"They knew that between the structural integrity of the building and the heavy fire conditions, there was no life that was sustainable inside. In the fire service, we risk a lot to save a lot, but we risk a little to save a little."

Despite the large fire, it remained a one-alarm call. Three aerials were raised, flowing thousands of gallons of water every minute, according to the department.

Other crews focused on preventing the fire from spreading to nearby businesses, the department said. The fire was brought under control in less than an hour, with a few crews remaining on the scene until later in the morning.

No injuries were reported, and the cause of the fire remains under investigation, the department said.