Firefighters were pouring water on the debris, but most of the dramatic fire had died down.

The fire started small in the basement of the warehouse near 39th Street and Park Avenue about 10:15. a.m. Wednesday. But it proved difficult for firefighters to find and contain in the smoky interior of the business, Park Warehouse Service at 3937 Park. The area is west of Cardinal Glennon Children’s Medical Center in the Botanical Heights neighborhood.

Eventually, firefighters were ordered out of the building by radio call and loud horn blast. About 11:30 a.m., there was a whooshing sound, and black smoke billowed out of the building’s doors and windows. Fire burst through the roof, and a wall on the south side of the building collapsed onto a firetruck.

Bricks and other debris littered the street around the firetruck, and aerial images showed the roof of the truck’s cab caved in, but no one was injured in the collapse. The pillar of black smoke was so thick it blocked out the sun.

“Very intense fire, burning for a long time,” said St. Louis Fire Capt. Garon Mosby. “Any structure is going to be weakened. Collapse was more or less imminent, and it happened sooner rather than later.”

Just minutes before, Mosby and members of the media had been standing in that area.

Mosby said a firefighter had injuries from smoke inhalation, but was treated and released from a hospital. At least a dozen workers were inside the building when the fire started, but they all escaped. One worker was taken to a hospital for treatment of smoke inhalation.

Mosby said Cardinal Glennon and St. Louis University hospital officials were notified of the smoke headed their way and advised to shut down their heating and air conditioning systems so that they would not pull the smoke inward.

Mosby said there were materials in the building that are hazardous when burned, such as Styrofoam products, and that officials planned to talk to the operators of the businesses at the warehouse to find out what other materials were stored there. Firefighters were initially warned that magnesium was stored in the building, but Mosby said that turned out to be false.

He said he knew of no evacuations of nearby homes or businesses.

Late Wednesday, the department tweeted a warning to neighbors about the possibility of inhaling dangerous chemicals from the fire. “If your home is in the path of the smoke plume, keep your windows closed and discontinue the usage of your HVAC system to reduce the amount of smoke drawn into your home,” it said.

Mosby said the most important part of that warning was keeping windows shut.

He also said anyone who already suffers from respiratory problems should be careful to avoid the smoke. For others, the risk wasn't known to be great, although avoiding the smoke was generally wise.

"Don't go walking outside if you don't have to be out," he urged.

The fire started on the south end of the building, which extends a block to the north. It was still burning and spreading as of 2:45 p.m., when Mosby said fire crews had learned about more than 150,000 citronella candles stored inside of the building. The fire had not yet gotten to the candles. Citronella is an essential oil primarily used as an insect repellent.

“That’s just fuel,” Mosby said when asked why they were concerned about the candles.

The smoke was visible from long distances, and a haze settled in the area of the hospital. SSM Health was giving patients, employees and visitors at the nearby hospitals face masks “out of an abundance of caution.”

Smoke, then evacuation

Mosby said the building dated to the 1920s. Part of the building has sprinkler systems, but the basement area where the fire was spreading may not. He described the basement, where the fire started and firefighters first tried to contain the blaze, as partitioned and maze-like.

Cara Papavramides said she worked in the building and was inside Wednesday morning when she noticed a burning, electrical smell. The lights started flickering, and smoke began coming out of electrical outlets. She said she started screaming for people to get out.

“It got bad within 10 seconds,” Papavramides said. “It was scary, but I’m glad everybody’s safe.”

Bob Grana, a part owner of the building, also works there at a freight logistics company. He said he was on the phone when he heard women screaming. He discovered smoke when he opened his office door and evacuated.

Numerous businesses leased space in the building. One of those companies, Reedy Press, is a small publisher that specializes in local interest and commemorative projects. Hundreds of copies of books by area authors went up in the plume of smoke seen across the city.

As the fire continued about 1 p.m., Patrick Davis stood watching the building. He had arrived early for a 1:30 p.m. job interview to find his potential workplace ablaze. Davis, 42, of St. Louis, said he was to interview for a second job as a forklift operator.

“I hope they haven’t lost the facility, with all that smoke billowing in the air,” he said.

Hours later, some in the neighborhood were outside watching the fire crews and police officers who remained at the smoky scene.

Roommates Kenzie Dillon, 25, and Katie Sorrick, 27, were among the onlookers. They moved to nearby Folsom Avenue last week.

Sorrick said she had seen windows burst on the warehouse and smoke pour out as she was being rerouted around the fire on her way to work earlier Wednesday.

"I just hoped that there weren't people in there," she said.

As she watched the smoke rise from the warehouse after 10 p.m., Dillon thought of two relatives who are St. Louis firefighters. "I'm very grateful to them right now," she said.

Nassim Benchaabane, Erin Heffernan, Ashley Jost and David Carson of the Post-Dispatch contributed to this report.