LOS ANGELES (AP) — Arson likely caused a massive weekend fire that has indefinitely closed a vital section of a freeway in Los Angeles, California Governor Gavin Newsom said Monday.

He did not say whether there were any suspects or persons of interest. The fire left the columns of Interstate 10 charred and chipped and the deck guardrails were twisted and blackened. 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.

Engineers were assessing the situation Monday. The freeway is used by 300,000 vehicles daily and the closure is expected to be felt well beyond the city, including possibly slowing the transport of goods from the twin ports of LA and Long Beach, federal officials have said. The ports are among the nation’s largest and handle more than half the goods coming into the US President Joe Biden had been briefed on the fire that erupted Saturday.

“We know that the origin of this is arson,” LA Mayor Karen Bass said. “We do not know other information.” She emphasised that there also is no reason to assume it was started by people who are homeless living under that section of freeway.

Bass acknowledged the havoc another closure of I-10 will have.

“It’s disrupting in every way, whether you are talking about traveling to and from work or your child care plans and the flow of goods and commerce, this will disrupt the lives of Angelenos,” Bass said. “So I will not settle for anything other than a rebuilding plan and a timeline that becomes a new model for speed.”

Los Angeles will be without a section of the freeway for an uncertain amount of time that caused damage reminiscent of the 1994 Northridge earthquake that flattened thoroughfares, officials warned Monday.

After the quake, it took more than two months to repair Interstate 10 and that was considered significantly fast.

“This isn’t going to be resolved in a couple of days, and it’s not going to take a couple years,” Federal Highway Administrator Shailen Bhatt told The Associated Press. “But whether it’s weeks or months, we’re still too early to tell.”

“The ports are still open and the goods will still flow, but when you remove a section of the interstate that carries 300,000 vehicles a day, there’s going to be spillover impacts,” Bhatt said. “The concern there is the quicker we can get this open, the faster we can remove an impediment.”

Bhatt said the fiery June 11 crash of a tractor-trailer hauling gasoline in Philadelphia that collapsed an elevated section of Interstate 95, snarling traffic and hurting area businesses, highlights what such disasters can do to not only a city but the nation. It reopened less than two weeks later due to a quick rebuild.

LA drivers were tested Monday during the first weekday commute following the raging fire beneath an elevated section of I-10. 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 were blasted with a predawn reminder for residents to plan different routes or expect significant delays.

Downtown LA seemed “more quiet than usual” on Monday, said Blair Besten, director of LA’s Historic Core business improvement district. She said she worried about another hit to businesses just emerging from the economic downturn due to the coronavirus pandemic lockdowns.

“I hope folks aren’t listening to leadership calling them to work from home!” Besten said. “Our businesses are just bouncing back from the Covid shutdowns. Business was just getting good.”

The cause of the fire Saturday is under investigation.

Flames reported around 12:20 am 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, city fire Chief Kristin Crowley said. No injuries were reported.

At least 16 homeless people living underneath the highway were evacuated and brought to shelters. Officials said there was no immediate indication that the blaze began at the encampment.

More than 160 firefighters responded to the blaze, which spread across 8 acres (3 hectares) and burned for three hours.

LA residents have a history of responding well to warnings of traffic troubles. Warnings of “Carmageddon” for a full freeway closure in 2011 resulted in a widespread reduction in traffic. A predicted “Jamzilla” in 2014 proved not to be monstrous, and fears of massive traffic snarls failed to materialise during the 1984 Olympics.

California Secretary of Transportation Toks Omishakin told a news conference Monday that two contractors have been hired — one to work on cleaning up the hazardous material under the freeway and the other to shore up the freeway.

Core samples were being tested from the superstructure, decks and columns to determine next steps but officials warned it was uncertain how long the repairs could take.

Repairs will require environmental waivers and federal funding, officials said.

In 2011, a fire from a poorly maintained fuel tanker that burst into flames damaged a stretch of State Route 60 — a key freeway connecting LA with its eastern suburbs — and took six months to reopen at a cost of $40 million.

“Please know that we’re determining the best course of action for getting this bridge back open as quickly and as safely as possible,” Omishakin said.

Omishakin said storage yards under highways are common statewide and across the country. He said the practice would be reevaluated following the fire.

Ertugrul Taciroglu, chair of the civil and environmental engineering department at the University of California Los Angeles, said “the unique challenge for these kinds of urban bridges is real estate is really expensive and hard to come by.”

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

Governor Gavin Newsom declared a state of emergency Saturday afternoon and directed the state Department of Transportation to request federal assistance.

The governor said Sunday that California 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.

Homeless encampments are also common sights near Southern California highways. In 2020, the city and county of Los Angeles agreed to provide housing for almost 7,000 people who lived under freeways and near exit and entrance ramps. In approving the deal, a federal judge said unhoused residents in those areas face particularly deadly hazards including pollutants and passing cars.