VideoPaul Kochli and Kate Burks were on their way home to Napa after a night of dancing in San Francisco early Sunday morning.

The couple had just finished crossing the Bay Bridge when they saw a large plume of smoke billowing into the sky.

"I told my girlfriend 'It looks like a plane crashed,'" Kochli said. "I saw huge flames (and) smoke and I could see that the freeway collapsed. I was in shock."

Burks and Kochli were fresh on the scene of a fiery accident that scorched the roadway and collapsed a stretch of Interstate 580 Sunday. Kochli pulled over and noticed that news crews had yet to arrive at the scene, he said.

"I knew I had my camera with me and I knew I had to get some shots," he said.

After Kochli shot about a minute of footage, police arrived and told him to move on, he said. Kochli turned his footage over to local and national TV crews, who had arrived several minutes after him. The footage was time-stamped at 4:05 a.m., Kochli said.

"I got it (the freeway) right after it collapsed," he said.

An overturned gasoline truck sparked the fire that closed the pair of freeway interchanges that skirt the east side of the San Francisco-Oakland Bay Bridge. Flames from the wreck caused part of one overpass to collapse on the other, officials said.

Authorities said the accident on a maze of highway ramps that provide access to the Bay Bridge and several other key freeways would cause the worst disruption for Bay Area commuters since the 1989 Loma Prieta earthquake damaged the bridge itself.

State transportation officials said it could take months to repair the damaged interchanges, and advised motorists to use public transportation into and out of San Francisco. They said that drivers who chose to take alternate routes on Monday would face nightmarish commutes.

"People are going to have to find a different way to work and back home in the evening so we are asking them to plan ahead and do their homework," said Jeff Weiss, a spokesman for the California Department of Transportation. "This isn't going to be fixed in a matter of days."

Although heat from the fire was intense enough to weaken the freeway and cause the collapse that damaged a stretch hundreds of yards long, the truck's driver walked away from the scene to a nearby gas station, Officer Trent Cross of the California Highway Patrol said.

The driver called a taxi that took him to a nearby hospital with second-degree burns, Cross said. No other injuries were reported, and officials said a major public safety disaster was averted only because the crash happened so early on a Sunday.

"I've never seen anything like it," Cross said of the stretch of crumpled interchange that was twisted into a mass of steel and concrete hundreds of feet long. "I'm looking at this thinking, 'Wow, no one died -- that's amazing. It's just very fortunate."

The crash occurred around 3:45 a.m. on the MacArthur Maze, a collection of interchanges on the edge of downtown Oakland about a half-mile from the Bay Bridge toll plaza. Although the bridge itself was not damaged, the labyrinth of three converging freeways delivers traffic to and from San Francisco and includes some of the Bay Area's most congested routes.

State transportation officials said that while only about 80,000 cars pass through the damaged interchanges each day, the ripple effect could inconvenience hundreds of thousands of motorists as drivers are forced to find ways around the closed routes. About 280,000 commuters take the Bay Bridge into and out of San Francisco each day.

"This will be one of the most problematic commutes in recent memory," San Francisco Mayor Gavin Newsom, speaking to reporters at the California Democratic Party convention in San Diego.

The tanker carrying 8,600 gallons of gasoline ignited around 3:45 a.m. after crashing into a guardrail on the interchange connecting westbound lanes of Interstate 80 to southbound Interstate 880. A preliminary investigation indicates the driver may have been speeding as he navigated the curving road, but neither alcohol nor drugs appeared to be a factor in the crash, Cross said.

The driver, whose name was not released, had a valid license and no history of driving under the influence, Cross said.

Heat from the flames exceeded 2,750 degrees and caused the steel beams holding up the interchange from eastbound I-80 to eastbound Interstate 580 above to buckle, and bolts holding the structure together to melt, leading to the collapse, California Department of Transportation director Will Kempton said.

Officials said that altogether a 250-yard portion of the upper roadway was damaged. The cost of the repairs would likely run into the tens of millions of dollars, and the agency was seeking federal disaster aid, Kempton said.

Witnesses reported flames from the blaze rose up to 200 feet into the air. The charred section of collapsed freeway was draped at a sharp angle onto the highway beneath, exposing a web of twisted metal beneath the concrete.

Newsom said the crash appeared to be an accident and that there was no evidence of foul play.

He said he had spoken to Gov. Arnold Schwarzenegger's administration and said he was assured the state would fast-track repairs, much as it did after the 1994 Northridge earthquake. He did not speculate about how long it might take to replace the span but predicted massive disruption to San Francisco Bay area traffic.

Schwarzenegger was to issue an emergency declaration later Sunday, a spokesman said.

Aides were still working out details, but a declaration will make it easier for the state Department of Transportation to issue contracts and avoid certain environmental reviews.

"It allows these repairs to happen much quicker," said Adam Mendelsohn, the governor's communications director.

Schwarzenegger was to arrive at the scene Sunday evening to survey the damage, he said.

Having portions of a main artery severed brought uncomfortably familiar images to the Bay Area. During the 1989 earthquake, both the Bay Bridge and section of Interstate 880 near the site of Sunday's collapse fell and crushed rush-hour motorists, leaving 40 people dead.

Newsom said Sunday's fiery crash showed how vulnerable the Bay area's transportation network is, whether to an earthquake or a terrorist attack. Sunday's freeway collapse has the potential to have a major economic effect on the city, he said.

"It's another giant wake-up call," said Newsom, who was preparing to leave the convention and fly back to San Francisco.

Dale Bonner, secretary for the state Business, Transportation and Housing Agency, said the accident posed immediate logistical and economic challenges. Sporting events scheduled in the Bay area Sunday included an afternoon Oakland A's game and evening NBA playoff game, both in Oakland.

"We're going to accelerate it as quickly as possible in a way that reflects the importance of these corridors, and we definitely want to keep the traffic moving in that area," he told The Associated Press.

He was planning to meet with regional transportation authorities later Sunday. They were to determine not only the scope of the damage but also seek a regional traffic plan while the interchanges are rebuilt.

On Sunday the collapse doubled the half-hour trip drivers normally face getting to and from San Francisco and the eastern suburbs -- even though many didn't even attempt the trip because of the crash. Traffic appeared light on the bridge itself, although motorists looking to get on and off were backed up on both sides.

Transportation officials said they already had added trains to the Bay Area Rapid Transit light rail system that takes commuters across San Francisco Bay and were urging people to telecommute if possible.

Transit agencies would work to press additional buses and trains into service to accommodate the expected jump in ridership, though the Bay Area's transit system already typically runs to maximum capacity, Metropolitan Transit Agency executive director Nathaniel Ford said.

The Associated Press contributed to this report.