A MASSIVE fire caused a bridge on the Interstate 85 road to collapse in the US city of Atlanta, closing the heavily-travelled highway.

Georgia governor Nathan Deal declared a state of emergency, saying every effort would be made keep traffic disruption to a minimum while emergency work continues.

Some 250,000 cars a day travel on what is a major artery for the US South and a thoroughfare for traffic heading north and south through Atlanta.

Georgia’s top transportation official, transportation commissioner Russell McMurry, said there was no way to tell when the highway could be safely reopened to traffic in either direction following the collapse, which happened during afternoon rush hour.

Firefighters noticed chunks of concrete falling from the bridge and got out of the way minutes before it collapsed.

“We will have to continue to evaluate the situation and adjust as we do,” transportation commissioner Russell McMurry said. “This incident - make no bones about it - will have a tremendous impact on travel.”

The bridge collapse effectively “puts a cork in the bottle,” Georgia state patrol commissioner Mark McDonough said.

The Metropolitan Atlanta Rapid Transit Authority plans to increase rail services and have additional staff on hand to help passengers reach their destination.

Atlanta mayor Kasim Reed said: “This is about as serious a transportation crisis as we can imagine."

Officials said no-one was hurt, despite dramatic images of towering flames and plumes of smoke.