A massive blaze ripped through a California warehouse early on Tuesday morning, causing the warehouse roof to collapse and firefighters to flee.

Several agencies responded to a warehouse operated by consumer goods company Kimberly-Clark around 12:30 a.m. near South Hellman Avenue and Merrill Avenue in Ontario, east of Los Angeles.

The massive fire engulfed the nearly-1.2 million square foot building, sending a smoke plume into the sky. Fire crews were shocked to discover an arsonist caused the blaze, who they said was a worker.

Dangerous conditions forced firefighters to flee as part of an “operational retreat,” Ontario Fire Department Deputy Chief Mike Wedell told The California Post.

Wedell said the “aggressive” fire overwhelmed firefighters as they made their first venture into the building, where they regrouped.

The six-alarm fire was so large neighboring fire agencies including San Bernardino County Fire Department had to intervene. About 140 firefighters battled the fire, which is still burning as of 8 a.m.

Wedell told the California Post that fire crews expected to be there for the better part of Tuesday. He said firefighters were having “great success” fighting the “extremely large” blaze.

Some fire engines had been peeling off the operation as the fire was quelled, Wedell noted.

The warehouse is worth around $156 million, according to Zillow.

An arson suspect, a male employee of the warehouse, has been arrested and is in Ontario police custody. The crime is still under investigation, officials told the California Post.

Paper products inside the building helped fuel the flames. Kimberly-Clark is a hygiene company that owns brands like Huggies and Kleenex.

The company told the California Post that there have been no reported injuries and the warehouse was operated by a third-party partner.

“We are aware of the fire at our distribution center in Ontario, California earlier today,” a Kimberly-Clark spokesperson told the California Post.

“Safety is our top priority, and we can confirm there are no reported injuries. The facility is operated by a third-party partner, and we are working closely with them and local authorities. We will share additional information as it becomes available.”

Other fire agencies like San Bernardino County Fire Department, Cal Fire/Riverside County Fire Department, Chino Fire Department, and the Riverside Fire Department assisted the fire efforts.

“The Ontario Fire Department is battling a 6 alarm warehouse fire. The building contains paper products. Units from many neighboring departments are on scene supporting the suppression efforts,” the San Bernardino County Fire Department wrote on X.

No injuries have been reported and employees have been evacuated. It’s unclear how the fire was set.

There was concern that the fire would spread, Wedell said, but the fire is now contained to the building.

Fire officials also noted that the air quality in the area would be impacted and children and seniors should stay inside.