A section of Interstate 95 collapsed Sunday after a large vehicle fire broke out beneath an overpass in Philadelphia, blocking travel in both directions, authorities said. There were no immediate reports of motorist injuries or fatalities, officials said.

Pennsylvania Gov. Josh Shapiro told reporters it would take "months" to repair the heavily-use interstate and that he plans to issue a disaster declaration Monday to expedite funds to hasten repairs. 

The incident happened shortly before 6:30 a.m. ET and triggered a multi-agency response from law enforcement and fire officials, who said they initially used a hazmat box as a precaution when they set out to extinguish the fire, which sent a plume of dark smoke rising up into the sky over Philadelphia. 

Shapiro said at a Sunday evening press conference that the source of the fire was a commercial truck believed to be carrying petroleum-based product and the blaze brought down an entire section of northbound lanes, Shapiro said.

The tanker was holding 8,500 gallons of gasoline when it caught fire, according to the U.S. Coast Guard, CBS Philadelphia reports.

Fire officials said the fire was under control as of 5 p.m.

Adjacent to the collapsed northbound section, officials said, the southbound side was "compromised" by excessive heat from the flames. Tumar Alexander, managing director for the city, told CBS Philadelphia that "I-95 will be impacted for a long time, for a long time."

At least one vehicle was still trapped underneath the collapsed portion of the highway, Shapiro said.

He said the incident caused "remarkable devastation" but that there were no reports of motorists on the interstate who were injured or died in the incident. Philadelphia Mayor Jim Kenney noted, however, that "the situation remains fluid."

Officials were still working on identifying any individuals who may have been caught in the fire at the collapse, the governor said.

CBS Philadelphia cites federal transportation records as saying the affected stretch of I-95 carries 160,000 vehicles a day on average. It is a main artery going north-to-south along the East Coast, said Michael Carroll, the Deputy Managing Director for Transportation in Philadelphia.

Officials said there was no threat to the city's water supply and that there were no concerns of any environmental impact from the incident. 

Government leaders in Philadelphia, at the state level and in Washington, D.C., were monitoring the situation and said they would coordinate plans to reconstruct the highway.

Leslie Richards, general manager at Southeastern Pennsylvania Transportation Authority (SEPTA), said that the city would be increasing regional rail capacity for certain trains to help alleviate the loss of the major roadway. She noted that transit ridership is still below where it was before the start of the COVID-19 pandemic, so there is already excess capacity.

Acknowledging the collapse in a tweet, Philadelphia Mayor Jim Kenney asked people to "avoid the area and plan for alternative routes of travel." Meanwhile U.S. Transportation Secretary Pete Buttigieg said he had already been in touch with Pennsylvania Gov. Josh Shapiro as well as partners at the Federal Highway Administration.

"Closely monitoring the fire and collapse on I-95 in Pennsylvania," Buttigieg tweeted. "I've been in touch with FHWA and spoke with Gov. Shapiro to offer any assistance that USDOT can provide to help with recovery and reconstruction."

The FHWA said in a statement Sunday it "has offered support and assistance to state and local officials to help them safely reopen this section of I-95 as quickly as possible," adding, "The FHWA Administrator will be joined by other FHWA experts in Philadelphia tomorrow to offer federal support and assistance."

"The President has been briefed on the collapse and White House officials have been in contact with Governor Shapiro and Mayor Kenney's offices to offer assistance," White House press secretary Karine Jean-Pierre tweeted.

The National Transportation Safety Board said it was sending a team to conduct a safety investigation into the fire and overpass collapse, in coordination with Pennsylvania State Police.

I-95 is a major interstate roadway running along the East Coast of the U.S. from Miami to the Canadian border in Maine. The section that collapsed on Sunday carries about 125,000 vehicles each day on average, CBS Philadelphia reported, citing federal transportation records.

While blocking traffic, the fire and subsequent roadway collapse has ignited broad environmental concerns, due in part to chemical emissions from the blaze affecting air quality in the area. A "code orange" — a warning that the air is considered unhealthy for sensitive groups, including children, older adults and others with certain preexisting medical conditions — was issued for areas in southwest Pennsylvania as a result of both the chemical emissions and the ongoing smoke infiltration from wildfires burning in eastern Canada.

The U.S. Coast Guard is also monitoring the potential for 8,500 gallons of vehicle fuel to leak into the nearby Delaware River.

"The tanker did leak a potential of 8,500 gallons of gasoline. However, most of it is shoreside," the Coast Guard said in a statement to CBS News on Sunday afternoon. Shoreside means the gas is mainly leaking on land, and the latest reports indicated it was "confined to the cove" beneath the overpass, according to the statement.

"Most of it is on scene, and it's going into the storm drains," the statement continued, noting that there was also "some leakage into the water."

"However, it's not enough to make a huge impact to the environment there," the Coast Guard said. "We're waiting to hear back from the pollution responders for the Coast Guard that are on scene. Usually when it's a small amount in the water, usually it'll dissipate itself."

Later Sunday, Shapiro said that there was a "slight sheen" at the entrance to a waterway, but that the leakage was quickly contained. 

Brendan Riley, director of water operations for the Philadelphia Water Department, also said Sunday evening the department had "no concerns of any environmental impact."

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