Arson was probably the cause of a raging fire over the weekend that has closed a mile-long stretch of the I-10, a major elevated interstate highway near downtown, the California governor said on Monday.

The California department of forestry and fire protection fire marshal made a preliminary determination that the fire was set intentionally, Gavin Newsom said during a press conference at the fire site. He said investigators had received some tips from witnesses but did not say if there were any suspects or persons of interest.

Newsom said investigators were trying to determine if one or more persons were involved. He gave no other details.

“I have to stress that we have determined what started the fire,” Newsom told reporters.

The closure has wreaked havoc for LA commuters and officials have warned commuters that they should expect traffic snarls as crews assess the damage to the route, which is typically used by 300,000 vehicles daily. It is not yet known whether the damaged portion will be repaired or demolished entirely, officials said.

“As we made clear yesterday, this was a huge fire and the damage will not be fixed in an instant,” said Karen Bass, the LA mayor, at a news conference on Monday morning. “Engineers have worked all night and are working right now to determine our path forward.”

Hazardous materials teams have taken samples of burned material to analyze, and will then remove debris from underneath I-10 to make way for engineers tasked with ensuring the columns and deck of the highway can support the vehicles that typically travel that route each day, officials said.

The interstate is the top priority of the state’s governor, Gavin Newsom, who visited the area on Sunday, said Toks Omishakin, the head of California’s transportation department.

Newsom said crews are working around the clock, but that officials could not yet offer a timeline for when the highway might reopen.

Preliminary samples taken from the highway deck found that it appears stronger than originally assessed but more structural analysis is under way, Newsom said on Monday.

Officials have urged commuters to use public transportation into downtown LA or work from home if possible as the closure will have ripple effects on other freeways and surface streets. Commuters should stay on freeways as surface streets will not be able to accommodate a surge of 300,000 people, Bass said.

“Losing this stretch of the 10 freeway will take time and money from people’s lives and businesses,” Bass said. “It’s disrupting in every way.”

The blaze was first reported around 12.20am Saturday when flames tore through a pallet yard in an industrial area under the highway. The fire spread to another pallet yard and burned parked cars, stacks of wooden pallets and support poles for high-tension power lines, the fire chief, Kristin Crowley, said. No injuries were reported. One of the damaged vehicles was a fire engine, the Los Angeles Times reported.

Pandemic-era sanitizer that was being stored under the freeway helped fuel the blaze, sources told the newspaper.

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.

Newsom declared a state of emergency on Saturday afternoon and directed the state department of transportation to request assistance from the federal government. Bass, said she had also talked with the US secretary of transportation, Pete Buttigieg, about any additional resources that may be needed.

The governor said on Sunday that the state had 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, but that the practice would be re-evaluated following the fire.

At least 16 unhoused 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, but misinformation spread in the aftermath blaming unhoused people.

“We know that the origin of this is arson,” Bass said. “We do not know other information. There is no reason to assume that the reason this fire happened is because there were unhoused individuals nearby.”

The mayor said the fire’s long-term impact could be reminiscent of damage from the Northridge earthquake that flattened freeways in 1994.

“Unfortunately, there is no reason to think that this is going to be over in a couple of days,” she said.