Meteorologist Mike Griesinger at the National Weather Service in Peachtree City said Saturday morning that it was indeed a tornado that hit downtown Atlanta.

The Friday night tornado may have seemed to strike Atlanta with no warning, but that's not true. The weather service issued a tornado warning about 12 minutes before the twister touched down in the city, Griesinger said.

"There was a warning," he said.

He said 12 minutes is about an average amount of time for a tornado warning. The warnings are sent out to local TV stations, weather radios, emergency management offices and cell phones programed to receive weather alerts. The TV stations typically air such warnings almost instantaneously, he said.

Rothfuse said more information will be released at a noon news conference at Station 4 on Edgewood Ave. Much of north Georgia, including metro Atlanta, is under a tornado watch until 7 p.m.

This morning's storm system came through with little power, Rothfuse said. "We got some hail in this system, but nothing big."

The NWS is now watching a storm system currently in north Mississippi. It should arrive in the metro area at about 3 p.m.

The storm hit fast and furious — and with little warning.

Shortly before 10 p.m., winds whirled through downtown Atlanta, taking aim at CNN Center, the Omni Hotel and the Georgia Dome, which was packed with thousands of Southeastern Conference basketball fans.

Hours later, at a 1:30 a.m. news conference at a fire station on Edgewood Avenue, Atlanta Mayor Shirley Franklin reported what weather officials had not yet done: that the damage was caused by a tornado.

"It's pretty major," Franklin said, flanked by fire, police and city officials. "... Most of us did not get any warnings in advance that this storm was brewing."

Another Franklin news conference has been scheduled for noon.

The bulk of the storm's wrath fell on the core of the city.

Sections of the Georgia Dome's roof were ripped off, forcing officials to move the four remaining games in the SEC men's basketball tournament — three on Saturday and one on Sunday — to Georgia Tech's Alexander Memorial Coliseum. Ticket holders will not be allowed in the arena, which seats just over 9,000.

Access to the remaining games of the tournament will be limited to athletes' family members, cheerleaders, bands and other credentialed individuals, the SEC announced.

Officials from the SEC, the schools remaining in the tourney and the Dome deliberated from midnight to roughly 4 a.m. Saturday before announcing a new schedule and ticket policy. Alexander seats 9,191 fans, much fewer than the 25,000 the Dome holds. Admission will be limited to players' families and anyone holding a working credential for the remaining games.

During the brief storm, a vacant two-story commercial building across from Centennial Olympic Park came down.

Two of the park's gigantic Olympic torches toppled over.

Massive pieces of metal siding peeled off a Marietta Street parking garage and wrapped around poles or clogged sidewalks and streets.

"I have not seen anything like this before," Atlanta fire Battalion Chief Gerry Rusinski said. "It looked like 9-11 when we pulled up."

Somehow, injuries seemed to be few and far between.

Four area hospitals, including Grady and Atlanta Medical Center, reported taking in 16 patients from the storm — most with minor injuries, though one reportedly in critical condition.

But there was concern about whether anyone was inside a four- or five-story building at the Stacks Lofts in Cabbagetown, where large chunks of four floors collapsed on top of each other like a pancake. Fire officials did not know whether anyone was inside the section that collapsed.

P.J. Bullock, 24, was having dinner with friends in a top-story unit at the time.

"We heard a huge breeze blow through," Bullock said. He said his dinner host tried to shut the window, but couldn't. "All of the sudden, the roof just ripped off."

The group ran out of the apartment before it collapsed.

"It was one of those things where you didn't know if you're going to make it out or not."

Around the same time, the two downtown basketball arenas were both holding games.

The Atlanta Hawks were playing in Philips Arena.

A few blocks away, Alabama and Mississippi State held court in the Georgia Dome.

John Hisey, 49, of Marietta, was at the Hawks game when the storm touched down.

"I heard a noise — it sounded like a big rumble," he said. "I looked up, and the wall was just flexing."

Some people hustled for the exits. "They just took off. They knew something," he said.

Sandy Smith of Douglasville was at the SEC tournament game. It had gone into overtime when she heard a loud boom. The ceiling started waving like a sheet.

"The lights started moving and the TV monitor started swaying back and forth," she said. Then a pole and sign tore a hole in the roof.

Outside, windows popped and shattered at the Omni Hotel. A billboard across from Olympic Park fell onto a car. Newspaper stands dropped in rows like dominos on sidewalks. Trees were pulled from the ground.

Raymond Sheffield, 34, of Dallas, Texas, was eating at Ted's Montana Grill on Spring Street downtown. Dessert had just arrived at his group's table when chunks of debris slammed into the glass front of the restaurant — shattering about half the windows and leaving the rest in sorry shape.

Darryll Douthard, 42, a valet parking attendant for the Thrive restaurant on Marietta Street, said one man drove into the parking garage as the storm hit.

As Douthard rushed him in a rear door, the man resisted, worrying about his car.

"Are you concerned with your car or your life? Douthard asked. "Get in the staircase!"

The storm passed in minutes. In both arenas, people started moving for the exits.

Marietta Street turned into a sea of bodies — many of them in basketball jerseys. Some were crying and visibly shaken. As authorities waited for city employees to clear debris off downtown streets, forecasters warned today's weather could be worse.

Friday's storm could be "nothing to compare with what's coming in tomorrow," said National Weather Service meteorologist Mike Leary.

Staff writers Chandler Brown, Chip Towers, Craig Schneider, Mike Knobler, Anisha Frizzell, Ben Smith, Andy Miller and Celine Bufkin contributed to this article.