A $4 million manatee house under construction at the Cincinnati Zoo and Botanical Gardens went up in flames Wednesday evening, creating dense columns of black smoke visible a mile from the fire.
No people or animals were injured in the five-alarm fire, but police were concerned about possible release of chemicals into the air.
Neighbors in Avondale heard a boom around 8 p.m., and police said there were propane tanks at the construction site.
Fire officials were trying to determine whether a 5-gallon can of kerosene in the building had caused the fire. A class of elementary-school students scheduled for an overnight visit were evacuated from the education building.
One firefighter was taken from the scene with a minor ankle injury.
"It looks like a lot of damage from the billowing smoke," said zoo director Ed Maruska, who was stuck outside waiting with other employees. The new building was scheduled to open in July.
"Terrible," Mr. Maruska said, looking upward at the billowing smoke. "It would have been more terrible if it had happened a month from today. It's a tragedy, but there's no loss of animals."
The zoo expected to be open today.
The zoo was expecting plenty of field trips in the coming days and weeks, said Zoo Academy senior Al Awtrey.
"It's bad," he said. "It's the end of the school year and we've got a lot of school groups coming in and out of here."
Construction workers left the site at 6 p.m. and firefighters were dispatched shortly after 8 p.m., said zoo spokeswoman Barbara Rish. The main body of the fire was knocked down by 10 p.m., but firefighters expected to be on the scene for quite some time.
Fire officials were moving cautiously, uncertain what chemicals were inside the structure. Neighbors, meanwhile, walked around surrounding streets as ashes rained down and marveled at all the smoke.
"I smelled something earlier, didn't think much of it," said Bruce Lewis, 35, a lifetime resident of the neighborhood. "But seeing all this smoke, this is serious, this has never happened like this before. To me this is pretty serious."
Geneva Brown, 72, who lives three blocks east of the zoo, saw the black smoke over the rooftops when she came outside for air between 8 and 8:30 p.m.
"When I saw the smoke from the house, I thought it was a storm cloud," she said. "I could smell it. Shingles burning, wood, or something."
Beatrice Seals, 64, another zoo neighbor, also saw the black cloud over the rooftops of her neighborhood when she went outside to smoke about 8 p.m.
"At first, before I saw the flames, I thought, "Oh, God, what kind of storm are we getting?' Then I saw the flame and thought, "Oh my Lord, the zoo is on fire.' "
Ms. Seals said the smoke was so bad that she had to go inside with her 15-year-old Siberian Husky, Mr. Lucky, who was wheezing.
"I had to go inside. If I had stayed out here, I would have had some breathing problems."
Police blocked off intersections around the zoo. The American Red Cross set up canteens and supplies for firefighters.
"Any time you have a disaster like this, there will be a negative effect. But the zoo will be fine," said Robert Sibcy, zoo board president.
Lisa Donovan, Phillip Pina, Saundra Amrhein, Kym Liebler and John Hopkins contributed to this report.
