(Updates with transportation commissioner comments on needed repairs, state storage site where fire broke out)
By Rich McKay
ATLANTA, March 31 (Reuters) - Georgia officials inspecting the fiery collapse of a major interstate highway bridge in Atlanta said on Friday the repair timetable was unclear but expect a "time-consuming event."
No casualties were reported after the span gave way on Thursday night as a fire raged beneath it, sending plumes of black smoke into the air and briefly setting off a fireball before the structure fell in on itself, snarling traffic.
State Transportation Commissioner Russell McMurry said on Friday that inspectors determined the southbound sections of Interstate 85 were so fire-damaged that they will need to be replaced. The state also plans to replace the collapsed section of the northbound bridge and possibly other adjacent sections, he said in a statement.
"At this time, we do not have an anticipated duration for the repairs ... but we do know that it is expected to be a time-consuming event," McMurry said.
As the fire raged on Thursday, the black smoke was so thick by the bridge in the heart of Atlanta that area residents told local reporters they thought a storm was coming or that the sun had set early when the fire started at around 6 p.m. EDT.
Flames shot up several stories from under the bridge before a section collapsed around 7:30 p.m., even as dozens of firefighters fought it, causing a brief fireball.
Hours after the collapse, drivers were still struggling to get off the highway. Republican Georgia Governor Nathan Deal declared a state of emergency for Fulton County, which encompasses much of the Atlanta area.
Government offices in Atlanta set a delayed opening for 10 a.m. on Friday to give people extra time to get to work.
Deal said the fire that led to the highway collapse appeared to have been fueled by a large pile of PVC piping under the structure.
The piping was being held in a state storage site for construction materials, said McMurry. The site is "a secured area" and PVC piping "is a stable, non-combustible material," McMurry said. (Additional reporting by Barbara Goldberg in New York and Dan Whitcomb in Los Angeles; Writing by Dan Whitcomb and Sharon Bernstein; Editing by Bill Rigby and Jeffrey Benkoe)