Fire officials said flames wiped out an entire city block in Richmond, Indiana on Tuesday morning.
Flames shot 60 feet into the air, forcing dozens of people to evacuate their homes.
Investigators also said the fire set off explosions of oxygen and propane tanks all over Northwest E Street between Third and Fourth streets.
The fire erupted around 4:30 a.m., causing thick black smoke in a business on the citys west side.
Firefighters called for mutual aid from neighboring fire departments, and it took almost 50 firefighters to bring the flames under control.
Fire officials said they expect to be on the scene all day. They said the flames erupted inside two construction companies and then spread to three other homes, destroying the businesses and two homes.
Investigators said about 10 or so other homes suffered heat damage from the fire.
Fire officials said no one suffered any injuries.