SANDY SPRINGS, Ga. -- Sandy Springs officials say a dam near The Falls apartment complex off Roswell Road is in imminent danger of collapse.

Sandy Springs Fire Department Assistant Chief Mark Duke said they first got a 911 call for a collapsed pedestrian bridge.

"At first, there was a big bang," resident Ruby McQueen said. "And the bridge collapsed. We saw all the [emergency] vehicles, and the water running. It was pretty frightening."

That walkway, often used by residents to access The Prado shopping center, was washed out by heavy rains. The collapsing concrete took out a gas line, and more than 100 residents were immediately evacuated. The dam holding back the quarter-acre pond has started to shift, and Duke said they're concerned it could completely collapse.

"I thought it was a gas main break," resident Matthew Taylor said. "I get around the corner of the road, I look back, and half the road is gone. It's pretty impressive."

The Red Cross set up an emergency shelter at the United Methodist Church on Mount Vernon Road. As of 8 a.m. Thursday, four families -- a total of 10 people -- had checked in.

Red Cross spokesperson Sherry Nicholson said the organization will help the displaced families throughout the day.

Road crews re-opened most of Roswell Road after engineers said the busy street was safe. One northbound remains closed and clogged with trucks and equipment.

Just before 6 a.m., Duke said it was still a "wait and see" situation. In the six hours since the collapse, he said the asphalt had continued to separate. Minutes later, a second pump arrived on scene. Crews will work to pump out the high waters pressuring the dam before they assess the damage and start repairs. As the work continues, lanes on Roswell Road will be periodically shut down.