A collapsed storm drain was the cause of a sinkhole that appeared Friday night on a Miami street, says a city official.

City work crews responded just before dark to what started out as a softball-sized hole in the vicinity of 222 G St. NE. Before long, that hole was widened at least six to eight feet in diameter as workers uncovered a sinkhole several feet deep.

(See photos in Monday's edition of the Miami News-Record.)

The street has since been reopened.

Miami Assistant Manager Tim Wilson blamed the cave-in on the collapse of a buried 24-30 inch clay drain tile.

What happens, Wilson said, is cracks develop in the underground pipe, which then sucks in the soil, fill material and bits of asphalt above it.

“Before too long, you may have a road on top and you can't tell visually that there's anything wrong, but there will be no support underneath,” Wilson said. “And one day it will just cave in.”

Wilson said freezing and thawing over the course of a winter make the cracks in the pipe even wider, resulting in more soil and fill material being sucked into it. The final collapse usually occurs in dry weather, as the pipe ultimately gives way.

He said much of Miami's drainage infrastructure dates back to the 30s and 40s.

“This happens from time to time, seems like every two or three years,” Wilson said.

City crews have filled in the hole with gravel. Once it's compacted, Wilson said, it would be re-asphalted.

Meanwhile, he said the street is “absolutely safe” to drive on.