ATLANTA (AP) — Atlanta's dreadful rush-hour traffic got even worse Friday, the morning after a raging fire underneath Interstate 85 collapsed an elevated portion of the highway and shut down the heavily traveled route through the heart of the city.

Traffic was bumper to bumper on nearby streets as drivers were forced to take a detour. Many commuters in some of Atlanta's densely populated northern suburbs will probably have to find new routes or ride mass transit for weeks or even months.

The blaze broke out Thursday afternoon in an area used to store construction materials, equipment and supplies, sending flames and smoke high into the air. Georgia Gov. Nathan Deal said PVC plastic materials in a vehicle may have caught fire.

Authorities were trying to determine how the blaze started.

Firefighters shut down the section of highway before it gave way, and no injuries were reported.

"This is about as serious a transportation crisis as we can imagine," Mayor Kasim Reed said.

I-85 carries 250,000 cars a day through the city and is one of the South's most important north-south routes.

Connie Bailey-Blake, of Dacula, 37 miles northeast of Atlanta, waited for a MARTA commuter train to reach her job in downtown Atlanta. She typically drives to work, often using the interstate.

"I'm supposed to be at work at 9 a.m. and it's 9:15 a.m.," Bailey-Blake said. "The first few days are going to be difficult. This will be my new life."

Amelia Ford picked another route to work by car and said it took her 45 minutes to travel 3 miles from her Atlanta home to the nearest open on-ramp to the interstate.

"It's actually pretty civil for morning commute traffic," Ford said by phone as she drove. "I think people kind of realize that there's not a whole bunch we can all do about it and we'll be dealing with it for months."

Georgia officials said there is no way to tell when the highway can be safely reopened in either direction. The northbound lanes collapsed, and the southbound side was also damaged.

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The governor said federal highway officials were providing assistance that will let crews immediately assess the damage and begin repairs. But he warned that it will be a long process, saying beams will have to be produced, tested, transported and installed.

The collapse effectively "puts a cork in the bottle," Georgia State Patrol Commissioner Mark McDonough said.

MARTA increased rail service and said it will have additional staff on hand to help passengers figure out how to get where they're going.

Bobby Barnhart, who works for a financial technology company near the interstate, said he and his colleagues watched the collapse from about 60 yards away. He said he heard several explosions, followed by a slow rumbling.

With the interstate closed, Barnhart said his morning commute was much more jammed than usual and took him about 30 minutes rather than the normal 10 to 15.

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AP video journalist Alex Sanz in Atlanta contributed to this report.

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