By Ellen Eldridge and Raisa Habersham

Georgia Gov. Nathan Deal declared a state of emergency Thursday night after fire officials extinguished a massive fire on I-85 in Atlanta that led to the collapse of a bridge on the interstate.

The bridge on I-85 northbound just south of Georgia State Route 400 near Piedmont Road collapsed about 7 p.m., Atlanta fire spokesman Sgt. Cortez Stafford said.

No injuries to motorists or first responders were reported.

Atlanta Mayor Kasim Reed said late Thursday he'd spoken with the FBI "and at this time there's no evidence of terrorism."

He said city officials will be working to assess the bridge throughout the night.

"This is as serious a transportation crisis as we could have. The governor has been leading and we have been acting on it," Reed said. "Our primary concern, first and most important, is that no one has lost their life. And as we stand here right now, we think that's the situation."

Stafford said a cause of the fire could not be determined at this time because inspectors could not get under the bridge yet due to structural concerns.

"The entire bridge is compromised," Stafford said. "Right now, it's still dangerous to go under there."

He said the cause of the fire was not yet known but "the speculation I've heard is that there are some PVC products that caught fire."

Witness James Shilkett was driving by the fire around 6:15 p.m. when he said he saw PVC piping on fire. Shilkett said two police officers were already on the scene and out of their squad car. Another police car arrived within one to two minutes, with fire engines another two or five minutes behind that, he said.

Capt. Mark Perry of the Georgia State Patrol said terrorism was not suspected.

Troopers based in Atlanta were working about 7:45 p.m. to get cars on the interstate turned around.

Hours after the collapse, the air stretching a quarter-mile north of the bridge was still acrid, spreading like a thin black fog.

All businesses surrounding the site were closed.

Atlanta police on the scene said it could be hours or days before the stretch of Piedmont is open again to traffic because authorities are concerned with potential structural damage.

"We've been so busy dealing with making sure the fire was out and that no lives were lost that we haven't moved to the traffic planning phase," Reed said. "There's a team at (the Georgia Department of Transportation) that's now working on that, and I'm confident that the governor will have answers (Friday) morning."

Rose Diggs lives less than a mile from the crash, but couldn't get home because Piedmont Road between Garson Drive and Lakeshore Drive was blocked.

"I have a handicap," she said, "and they're saying I have to walk, but it's raining and dark."

Michael Brooks, 43, was heading home on I-85 when he saw the smoke.

"I thought it was a terrible wreck. Vehicles stopped suddenly," said Brooks, who works at CNN.

People started getting out of their cars. They said, "the bridge is going to collapse."

Brooks said he sat there for 2 { hours. As for Friday, he said about getting to work, "I guess I'll figure that out some way."

GDOT spokeswoman Natalie Dale said the interstate will be closed in both directions "for the foreseeable future."

The collapse of a major interstate through Atlanta is sure to scramble commerce. Companies were contemplating their next moves.

A spokeswoman for Atlanta-based delivery giant UPS said the company's contingency planners were assessing the I-85 situation "to define our activity, routing."

While many interstate tractor-trailer drivers use I-285, rather than taking I-85 through the city, the closing of I-85 will certainly push traffic onto other interstates, potentially scrambling traffic there.

Delta Air Lines said it will "work with customers on a case-by-case basis to accommodate them if they're running late as a result of any ensuing traffic issues."

The Atlanta-based airline also said it encourages its employees to monitor traffic reports and "use their best judgment in safely commuting to their jobs," spokesman Morgan Durrant said.

"It's a massive productivity issue," said Brian McGowan, a former CEO of Atlanta's economic development arm and now a principal in the public policy and regulation practice at law firm Dentons. "You are going to have hundreds or thousands of companies who can't get their employees to work on time."

The public sector will also take a blow as tens of thousands of government workers will be affected.

McGowan said the short-term potential losses are substantial. It will disrupt businesses' supply chains. Families will have to re-think how they travel around the city.

Companies that don't encourage telecommuting should, while others should look to expand their programs or dust off plans that have been on a shelf, McGowan said.

The flames started underneath the interstate. Fire officials asked drivers in the area to keep their windows closed.

Paula Pontes, a resident of the Peninsula at Buckhead, said when her home went dark she thought it was an incoming storm.

"It got dark all of a sudden so I turned on the news to see if it was the rain," Pontes told The Atlanta Journal-Constitution.

She said she never heard an explosion and couldn't see flames, but it smelled like burnt rubber.

"I didn't panic because I couldn't see the fire coming," she said. "It was just smoke. It became night."

The Georgia Department of Public Health said wind pushed smoke into other areas, but there was "no significant toxicity identified in the smoke."

(Staff writers David Wickert, Rhonda Cook, Matt Kempner, Scott Trubey, Christian Boone, Marlon Walker, Meris Lutz, Leon Stafford, Kelly Yamanouchi, Rosalind Bentley and Greg Bluestein contributed to this article.)

(c)2017 The Atlanta Journal-Constitution (Atlanta, Ga.)