PG&E Corp. shares on Thursday ended at their lowest in more than 15 years on growing concerns that the utility’s insurance may not cover the possible losses from the worst wildfire in California history.

Stock of the parent of Pacific Gas and Electric PCG, -1.30% , with about 16 million customers in California, ended down 31% at $17.74 on Thursday, its lowest close since June 2003 and its largest one-day percentage loss since April 2001.

The company’s bonds also have tumbled this week, although they recovered a bit of ground on Thursday.

California regulators are still investigating the cause of what’s called the Camp Fire that has blazed across roughly 140,000 acres in Butte County, Northern California.

The death toll has risen to 56, with about 100 people missing. The fire is 40% contained, according to the California Department of Forestry and Fire Protection, or Cal Fire, on Thursday. It has destroyed nearly 9,000 structures, mostly homes, and remained active overnight. The fire is not expected to be fully contained until Nov. 30.

Analysts at Morgan Stanley on Thursday downgraded PG&E stock to their equivalent of neutral and slashed their price target on the shares, citing “major investment uncertainties” about the company, including questions around liquidity and “persistent” fire risk.

The analysts, led by Stephen Byrd, cut their price target to $31 from $67.

Also Thursday, analysts at Mizuho lowered their price target on PG&E shares to $27 from $48, representing 35% upside over current share prices.

They kept their rating on the stock at neutral, saying they estimated a potential after-tax liability exposure from the Camp Fire of up to $13 billion, which could be offset by $1.4 billion in insurance coverage disclosed by the company in a Tuesday regulatory filing.

“Bigger question relates to PG&E’s ability to pay its contractual spending obligations related to the company’s $6.0 billion annual construction program,” they said.

In the filing on Tuesday, PG&E said the outage happened in the area of Butte County near the city of Paradise where the fire is understood to have started. Paradise was all but completely wiped out in the blaze.

PG&E warned that while it had renewed its liability insurance coverage for wildfire events in its most recent quarter to an aggregate amount of about $1.4 billion, it could be facing a far larger bill that would have serious implications for its finances.

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“While the cause of the Camp Fire is still under investigation, if the Utility’s equipment is determined to be the cause, the Utility could be subject to significant liability in excess of insurance coverage that would be expected to have a material impact on PG&E Corporation’s and the Utility’s financial condition, results of operations, liquidity, and cash flows,” the company said in the filing.

PG&E said it notified the California Public Utilities Commission of the failure of some of its equipment in an electric incident report on Nov. 8. The report said the failure began at about 0615 hours. The fire is reported to have started at 6.33 a.m., according to Cal Fire.

PG&E is already facing liabilities from wildfires that raged in 2017, destroying more than 245,000 acres. In its most recent earnings report, the company said it was guiding for $1.65 billion to $1.82 billion in after-tax costs related to 14 of the 2017 fires, net of insurance and other costs. State investigators have linked PG&E’s equipment to about 17 of the 2017 fires, according to a regulatory filing from Nov. 5.

Tim Hynes, head of North American research at Debtwire, said Wednesday that the stock selloff had wiped about $12 billion off the company’s market cap. “It’s fair to assume that that’s what the market is expecting the liability to be,” he said.

But PG&E has no near-term debt maturities or liquidity issues and the liability will be dealt with over years. “If there were a near-term risk, the stock would have sold off even more,” he said.

PG&E has said it believes the increase in wildfires in recent years is closely tied to global warming, the result of much drier conditions after recent droughts and hot weather. That is a credible argument, said Hynes.

“The company has been around for more than 100 years and its equipment has not caused wildfires like this in the past,” he said.

It may also get help from the state of California, which intervened in 2001 when PG&E was forced into bankruptcy during the power crisis created by Enron, he said.

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MKM Partners said Wednesday that insurers are bracing for more catastrophe losses from all three of the wildfires currently burning in the Golden State.

The Woolsey Fire burning in Los Angeles and Ventura counties has destroyed 98,362 acres and is 57% contained, according to Cal Fire on Thursday. The Hill Fire has destroyed 4,531 acres in Ventura County but is 97% contained.

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“While the rainy season in Northern California is expected to begin soon, it could be a while before Southern California sees some relief,” analyst Harry Fong wrote in a note. “Insurers have already paid hefty sums for the 2018 California fires, by some estimates upwards of $1.5 billion through the third quarter, and it could exceed this level in the fourth quarter.”

Fong is not expecting this year’s losses to reach the levels seen last year with total fire losses of about $13.5 billion.

PG&E’s shares are down about 56% in 2018, while the S&P 500 SPX, +0.51% has gained 0.7% and the Dow Jones Industrial Average DJIA, +0.29% has gained 0.9%.

Spreads on the company’s 6.050% notes that mature in March of 2034 tightened by 31 basis points Thursday to 351 basis points over comparable Treasurys, according to MarketAxess. The notes were last trading at 92.500 cents on the dollar to yield 6.848%.

PG&E’s 3.300% notes that mature in December of 2027 saw spreads tighten by 15 basis points to 317 basis points over Treasurys. Those notes were trading at 81 cents on the dollar to yield 6.263%.

The company has about $18.4 billion in long-term debt, according to FactSet data.

See also:Fast-moving Northern California wildfire prompts more than 25,000 evacuations

Claudia Assis in San Francisco contributed to this report