Note: Our coverage of the 10 Freeway closure has moved here.
There was no immediate information on a possible arson suspect or suspects, but Newsom said the fire was set within the fenceline of the storage business operating below the freeway, which was littered with vehicles, pallets and other materials.
"That determination of who is responsible is an investigation that is ongoing, and that's an investigation that can be aided by the people of the region, not just those that have been witnesses nearby," said Newsom.
The governor also said that the structural assessment of the freeway is ongoing and that "the structural integrity of the deck appears to be much stronger than originally assessed."
However, Newsom was quick to point out that this does not mean a demolition of that portion of the 10 Freeway is off the table, and officials are continuing their assessment.
Over 100 columns were damaged, according to officials, at least 9 of those severely.
"We'll continue the bracing work as we conduct subsequent sample testing," said the governor. "That subsequent sample testing should be back first thing tomorrow morning, and will allow us to make a subsequent announce of whether or not we're tearing this down and replacing it, or we're continuing the retrofit and repairs and the bracing."
Bracing and retrofitting would allow officials to open the freeway much sooner than a complete demolition and repair.
Anyone with information regarding this investigation is urged to call the CAL FIRE Arson Hotline at 800-468-4408.
Southern California drivers, warned of potentially terrible traffic snarls, headed into the Monday morning commute following a raging pallet fire over the weekend that closed a portion of the 10 Freeway.
MORE | 10 Freeway closure in DTLA creates giant headache for rideshare drivers
10 Freeway closure in DTLA creates giant headache for rideshare drivers
Many commuters appeared to have heeded the warnings.
"In looking at the traffic data earlier this morning, I am somewhat pleased to say that the congestion was a little bit lighter than normal," said Rafael Molina, deputy district director for the division of traffic at the California Department of Transportation. "However, please - if you don't need to be in downtown Los Angeles - please avoid those trips."
Cellphones blasted a predawn reminder for residents to plan alternate commuting routes and to expect significant delays due to the fire's impact on the freeway.
Why is the 10 Freeway closed?
Hazardous materials teams were clearing burned material from underneath the freeway to make way for engineers who will ensure the columns and deck of the structure can support the 300,000 vehicles that typically travel that route daily, Gov. Gavin Newsom said at a news conference Sunday.
"Remember, this is an investigation as to the cause of how this occurred, as well as a hazmat and structural engineering question," Newsom said. "Can you open a few lanes? Can you retrofit the columns? Is the bridge deck intact to allow for a few lanes to remain open again?"
Newsom said answering those questions would be a "24-7 operation," but officials couldn't yet offer a timeline for when the highway might reopen.
Where is the 10 Freeway closed?
Commuters were urged to work from home or take public transportation into or around downtown L.A. The mile-long closure between Alameda Street and the East Los Angeles Interchange will have ripple effects on surface streets and other key freeways, the California Highway Patrol said.
WATCH | What does traffic look like on DTLA streets? Here's a firsthand look
What does traffic look like on DTLA streets? Here's a firsthand look
What are the detours around the 10 Freeway?
L.A. transportation officials urged drivers to transfer to other freeways -- like the 60, 5 and 101 -- instead of getting off the freeway to get around the closure using surface streets.
Commuters brace for traffic nightmare as 10 Freeway remains closed in downtown LA
Doug Young, an assistant chief with the CHP, provided the following freeway detours:
-- drivers on eastbound 10 Freeway will be diverted at Alameda Street;
-- drivers on the westbound 60 will be diverted to northbound 5 or northbound 101;
-- drivers on southbound 5 will be diverted onto the westbound 10 but must take the first exit at Mateo Street;
-- drivers on northbound 5 must divert to the northbound 101.
Metro released a comprehensive list of public-transit alternatives, and residents were advised to visit emergency.lacity.gov for updates.
Anyone planning to attend major sporting events in or around downtown L.A. may want to seek an alternate route or plan for major delays, according to Caltrans.
Metrolink said it will expand service beginning Monday on its San Bernardino Line to support travelers impacted by the freeway closure. The agency will increase capacity and run added service on the line to and from the Inland Empire and downtown L.A. Six extra trains will run in each direction: three in the morning and three in the afternoon and evening.
Investigation continues into cause of fire that caused 10 Freeway shutdown
What caused the 10 Freeway fire?
At a mid-morning briefing Monday at Caltrans District 7 headquarters, Toks Omishakin, the state's secretary of transportation, announced that the state fire marshal's office completed its investigation into the fire about 6 p.m. Sunday and allowed Caltrans engineers full access to the site.
Omishakin said emergency funding was in place, and two contractors have been working at the site to clean up the area and shore up the structure. Core samples were taken of concrete and rebar, and engineers were working to analyze the samples and develop a course of action -- essentially determining if the damaged columns and freeway can be repair or if a complete rebuild will be required, Omishakin said.
Omishakin said it was "too early to say how the fire started."
Flames reported around 12:20 a.m. Saturday ripped through two storage lots in an industrial area beneath the highway, burning parked cars, stacks of wooden pallets and support poles for high-tension power lines, fire Chief Kristin Crowley said. No injuries were reported.
More than 160 firefighters from more than two dozen companies responded to the blaze, which spread across 8 acres - the equivalent of about six football fields - and burned for three hours. The highway's columns are charred and chipped, and guardrails along the deck are twisted and blackened.
The governor said Sunday that the state has been in litigation with 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 subleasing the space.
"This is a site we were aware of, this is a lessee we were aware of," he said.
Omishakin said storage yards under highways are common statewide and across the country. He said the practice would be reevaluated following the fire.
At least 16 homeless people living underneath the highway were evacuated and brought to shelters, Bass said. Officials said there was no immediate indication that the blaze began at the encampment.
The mayor said the fire's long-term impact could be reminiscent of damage from the Northridge earthquake that flattened freeways in 1994.
When will the 10 Freeway reopen?
More than 48 hours after it started, officials could not provide an estimated reopening time for the damaged freeway.
"As we made clear yesterday, this was a huge fire and the damage will not be fixed in an instant," Bass said during a press conference Monday morning. "Engineers have worked all night and are working right now to determine our path forward."
Caltrans has secured a $3 million emergency contract to test and clear hazardous material from the site, as well as to help fix the damage.
"We're seeing a lot of... concrete that's flaked off the columns. The underside of the bridge deck may be compromised," Caltrans spokesperson Lauren Wonder said over the weekend. "It's sort of a waiting situation right now. We don't have an estimated time of opening but Caltrans wants to ensure that this bridge is safe to put traffic back on it."
Mayor Karen Bass, Gov. Newsom provide update on 10 Freeway closure
Mayor Karen Bass, Gov. Gavin Newsom provide update on 10 Freeway closure
"What appears on the outside to be problematic may not be the real problem. It's what lies underneath and that's the bridge deck," said Newson. "That's the primary focus now of our investigation."
LAUSD schools to remain open
"All schools and offices will remain open," L.A. Unified School District Superintendent Alberto Carvalho said at a news conference. "For families whose students use school bus transportation, the schedule of your route could be impacted by the closure of the 10 Freeway, but service will continue to be provided. Specific information will be provided directly to families by our Transportation Services Division this afternoon and tomorrow morning. Families who have questions about district transportation are encouraged to contact 1- 800-LA-BUSES (522-8737)."
Carvalho also said that several schools will be impacted from the closure, and he cited students coming from Boyle Heights as significantly affected.
The Associated Press and City News Service contributed to this report.