State fire officials made a preliminary determination that the ignition of the huge fire that engulfed a section of Interstate 10 after midnight was caused with malicious intent and was a criminal act of arson, California Gov. Gavin Newsom announced Monday.

Newsom said investigators are trying to determine if one person or more were involved. He gave no other details but urged the public to call a confidential line with any information that could lead to the determination of who was responsible.

"I have to stress that we have determined what started the fire," Newsom told reporters. Commuters to downtown Los Angeles were urged to take public transportation or work from home on Monday morning as the city braced for major transportation disruptions after a huge fire engulfed a section of Interstate 10 after midnight on Saturday.

The blaze left many columns charred and chipped and the deck guardrails twisted. Crews shored up the most damaged section for the safety of workers clearing the debris. It’s still unclear what structural damage, if any, the blaze caused to the freeway.

The highway remained closed on Monday between Alameda Street and the East L.A. Interchange, according to the California Department of Transportation. The highway will be closed to commuters indefinitely and it's unknown how long the repair or replacement could come, Newsom added.

The California Department of Transportation is working to determine the structural integrity of the bridge, said California State Secretary of Transportation Toks Omishakin.

Newsom said officials will make an announcement Tuesday whether the state "will be tearing the structure down and replacing it or continuing the retrofit and repairs and the bracing."

"The basis will be determined on safety and not just speed," said Newsom. "The worst thing we can do is make bad short-term decisions."

Los Angeles Mayor: 'Being stuck in traffic is something that makes Angelenos angry'

In a message to Los Angeles residents, Mayor Karen Bass at the news conference said: "In this time of crisis and in this time of emergency, we need to pull together. Being stuck in traffic is something that makes Angelenos angry. We will do everything we can and work 24 hours a day until we settle this."

Earlier in the day, Bass explained that "losing this stretch of the 10 freeway will take time and money from people's lives and businesses."

Department officials advised commuters to work from home or take public transportation if possible.

"We will need this to be able to relieve congestion and get people from Santa Monica to San Bernardino and back," said Omishakin.

Drivers using the interstate should stay on the freeway and avoid local streets, according to Los Angeles Department of Transportation General Manager Laura Rubio-Cornejo.

Those with destinations in the downtown area should use "surface streets," she said. The department also deployed officers to downtown streets to direct the flow of traffic.

"It is critical that drivers heed the signs and traffic officer instructions in order to maintain the safe movement of people through the impacted area," Rubio-Cornejo said.

Commuters should use the E, J or A Line Metro trains to access downtown Los Angeles, Los Angeles County MTA CEO Stephanie Wiggins said. Metrolink also increased train service from Covina to the downtown area, she said.

LA schools chief: Expect delays 'impacting a significant number of students'

Schools were open Monday in Los Angeles despite the freeway closures but schools downtown will be affected, Los Angeles Unified Superintendent Alberto Carvalho said Sunday. They include Ninth Street Elementary School, 20th Street Elementary School, Metropolitan Continuation High School, Inner-City Arts, and Para Los Niños Charter School.

Carvalho said some school bus routes were slated to change, NBC 4 Los Angeles reported. On Monday, he indicated effects could be widespread ‒ and last for a while.

"We expect some degree of delay impacting a significant number of students over the next days and perhaps weeks," Carvalho in a post on X, formerly known as Twitter. "We will continue to provide support to our school communities."

Commuters tested after long delays

Drivers were tested Monday during the first weekday commute since the raging fire. Some freeway exits backed up as drivers were forced to use crowded surface streets to bypass the damaged freeway stretch south of downtown.

Some routes, however, had lighter traffic, suggesting drivers heeded warnings from the city to make alternate plans. Cellphones blasted Monday with a predawn reminder for residents to plan different routes or expect significant delays.

"Our businesses are just bouncing back from the Covid shutdowns. Business was just getting good," said Blair Besten, director of LA’s Historic Core business improvement district. She’s worried about the lingering effects of this closure.

Storage yards under California highways

California Fire Marshal Daniel Berlant said investigators have identified where the fire started and what the cause was after sorting through the rubble for evidence but did not specify what they found. He said they are talking to witnesses, including homeless people and nearby business owners.

Storage yards under highways are common statewide, with the money from the leases going to public transit. Newsom said the practice would be reevaluated following the fire.

The governor said California has been in litigation with Apex Development, Inc., the owner of the business leasing the storage property where the fire started. The lease is expired, Newsom said, and the business had been in arrears while illegally subleasing the space to five or six other entities. "They’ve been out of compliance for some time, that’s why we’re going to court" early next year, he said.

Mainak D’Attaray, an attorney for Apex Development, confirmed the company was in litigation with the state.

“We are currently investigating ourselves what happened at the yard under the freeway. As such, we are not prepared to give an official statement or answer questions until we have determined what actually occurred,” D’Attaray said in an email.

Ertugrul Taciroglu, chair of the civil and environmental engineering department at the University of California, Los Angeles, said part of the challenge is how expensive real estate has become.

“Every piece of land is being utilized, so I can see the pressure or the incentives for making use of these spaces under these highways,” he said.

Engineers work overnight as repair process begins

Bass said the fire caused heavy damage but promised that the rebuilding plan would become "a new model for speed."

"This was a huge fire and the damage will not be fixed in an instant," she said.

Engineers worked overnight to assess highway damage and kick off the repair process, Omishakin said. "If you're wondering whether or not there's any activity on the site of the incident, as we speak, all through the night, through the morning, our maintenance and structural folks are there doing work."

Omishakin also said authorities would determine in the next couple of days if a full demolition of the remaining strip of highway was necessary to fully repair the bridge.

"The shoring for the bridge is up. They did that all through the night," he said.

The blaze broke out on an industrial stretch of the interstate that more than 300,000 commuters use every day, making it one of the most traveled freeways in the country. Newsom declared a state of emergency on Saturday night.

No one was injured and no homes were damaged, officials said on Sunday, but 16 unhoused people living under the bridge evacuated. The fire may have displaced more, Bass said.

Cybele Mayes-Osterman is a breaking news reporter for USA TODAY. Reach her on email at [email protected]. Follow her on X @CybeleMO.

Contributing: Vanessa Arredondo, USA TODAY; The Associated Press