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Three men were injured in an explosion as heavy fire engulfed a business in the industrial district of downtown Los Angeles Saturday, the Los Angeles Fire Department said.

The blaze was reported about 12 p.m. at 743 Kohler St. and firefighters started a defensive firefighting operation as soon as they arrived at the scene, making sure the flames don’t spread to neighboring structures, according to an LAFD alert.

Two of those injured suffered severe burns and were hospitalized in critical condition. A third person was hospitalized in fair condition.

A total of 140 firefighters responded to what the department called a “Major Emergency fire.” They put out the blaze about an hour later.

“The fire building only sustained serious damage from at least one explosion that occurred prior to LAFD arrival,” the department said.

The structure on fire was described as a 50-feet-by-100-feet, one-story business in a row of commercial structures. It was not clear what type of business the fire originated in.

Firefighters were greeted with heavy smoke and flames, Capt. Branden Silverman told KTLA.

“The firefighters were not able to make immediate entry due to the fact that there was such heavy fire involvement, and there were subsequent smaller explosions going on,
So they immediately went into defensive operations to protect the adjoining business,” he said.

A photo released by the fire department showed flames burning inside a small building with debris littering the ground outside as a firefighters worked. A sign that reads “Radix” could be seen on the building.

Witnesses shared videos of thick smoke billowing over downtown L.A., with one describing hearing a “big boom” then seeing flames.

The proprietor of a nearby tattoo shop who identified himself as Angel said he witnessed the blast and aftermath. After hearing the explosion and running outside, he saw a man lying injured at the entrance to what appeared to be a warehouse.

“I’ve never been in an explosion before,” he said. “The impact blew me back several feet. I felt the glass shatter and hit me. I even felt the heat from the explosion, the fireball, hit me and kind of singe my arms a little bit.”

It’s unclear what triggered the apparent explosion and fire. An investigation was ongoing.

No additional injuries were reported and no further details were immediately available.

KTLA’s Brian Day contributed to this report.