Fire officials said the blaze, which broke out about 1 p.m. near downtown Indianapolis and forced the evacuation of nearby homes, may not be extinguished until Monday, The Indianapolis Star reported.
"This is a very dangerous situation," city police spokesman Christopher Wilburn said. "Dangerous to breath the smoke and dangerous because we don't know what the fire is going to do."
One firefighter suffered a minor injury.
A third of the 400-square-foot Nationwide Recycling warehouse's roof had collapsed by late afternoon. The newspaper said several explosions were heard, possibly from trucks and propane tanks stored inside.