ATLANTA — Alabama and Mississippi State were locked in a thrilling game at the Southeastern Conference tournament. Suddenly, everyone started looking toward the roof of the Georgia Dome, wondering where that rumbling sound was coming from.

What they saw was terrifying.

Metal scaffolding and a temporary video board swaying back and forth. The huge fabric roof flapping like a flag in a stiff breeze. Two large panels above the upper deck starting to peel away. Small chunks of insulation and debris drifting toward the court.

A possible tornado, said the National Weather Service.

No doubt about it, said those who went through it — players, coaches and some 18,000 fans.

"I thought it was a tornado or a terrorist attack," said Mississippi State guard Ben Hansbrough, who was guarding Alabama's Mykal Riley when the clatter began above their heads, growing into an angry growl that, yes, sounded like an approaching freight train.

The storm forced the SEC to take the unprecedented step of moving the rest of the tournament to Georgia Tech's Alexander Memorial Coliseum. Because of the smaller capacity — 9,100 compared with the dome's basketball capacity of 26,000 — there was no way to divvy up the tickets and keep everyone happy.

So, only players' families, cheerleaders, bands and those with working credentials will be allowed to attend, probably no more than 2,000 per game. It will be a surreal setting for the remaining games and surely cause plenty of backlash from schools — especially Kentucky — that had tens of thousands of boosters in the city.

The Wildcats faithful didn't even get a chance to see their team play.

"We're hopeful that fans will realize what happened tonight," said SEC associate commissioner Charles Bloom, adding there would be a refund policy. "But we know there will be some frustration for the fans."

The storm struck while Alabama and Mississippi State were in overtime of their quarterfinal game. They were able to finish after a delay of just more than an hour — Mississippi State won 69-67 — but the SEC called off Georgia-Kentucky because of concerns that more strong cells were closing in on the city and the building may have sustained structural damage.

Now, either Georgia or Kentucky will have to play a doubleheader Saturday. They will meet at noon EDT, with the winner facing Mississippi State about nine hours later. Tennessee and Arkansas will meet in the other semifinal, scheduled for 6 p.m. Saturday.

"A major, major challenge" is how Georgia coach Dennis Felton described it on his way out of the dome.

The championship will be played Sunday, as planned, but two hours later at 3 p.m.

Earlier Friday, two quarterfinal games were played without any problems. No. 4 Tennessee, the regular-season champion, avoided a major upset when Chris Lofton hit a 3-pointer with 11.4 seconds remaining for an 89-87 victory over South Carolina. The Volunteers advanced to face Arkansas, an 81-75 winner over No. 18 Vanderbilt.

The evening session was anything but routine. National Weather Service officials called the storm a possible tornado, and winds were clocked at up to 60 mph as it moved through the city.

"We planned for a lot of things," Mississippi State coach Rick Stansbury said. "We didn't plan for a tornado."

While the weather service waffled on whether a tornado struck the 16-year-old dome, everyone sure felt that's what they had been through after a loud, rumbling noise swept over the building. The damage was especially striking on the outside, where large chunks of insulation and metal panels — some as long as 25 feet long — were ripped off the building.

There were no reports of injuries inside the stadium, Bloom said.

The Alabama-Mississippi State game was stopped with the Bulldogs leading 64-61 and 2:11 left in overtime. Both teams were sent to the locker room and some fans fled for the exits, worried that the roof might cave in. Alabama coach Mark Gottfried found his family members in the stands and hustled them to safety.

"I looked up," Gottfried said. "I could see everything swaying."

Those who remained in their seats looked anxiously at the Teflon-coated Fiberglas fabric roof, which is designed to flex slightly during high winds but was rippling heavily in the storm.

Bloom said the building was deemed structurally sound when Alabama and Mississippi State resumed play, though huge chunks of debris were piled up on the sidewalks surrounding the 70,000-seat stadium — normally home of the NFL's Atlanta Falcons — and a breeze could be felt blowing through the inside.

Several fans and at least one reporter on press row said metal bolts and washers fell from the ceiling. A pipe ripped a hole in the roof away from the court, which is set up at one end of the dome in a smaller configuration for basketball.

There was no announcement during the game that a strong storm was approaching, but several fans got advance warning on their cell phones.

"The guy behind me got a phone call saying there was a tornado warning," said Lisa Lynn of Atlanta, who was watching the game from the lower deck. "And in 2 seconds, we heard the noise and things started to shake. It was creepy."

Thousands of fans were downtown for two sporting events. An NBA game between the Atlanta Hawks and Los Angeles Clippers was held next door at Philips Arena, which reported no major damage. But numerous windows in CNN Center, headquarters of the cable news network and part of the same complex, were blown out.

The Georgia Dome, which is as tall as a 29-story building, had the largest cable-supported roof in the world when it opened in 1992. Heavy rains caused a leak three years later, leading to a structural adjustment that prevented a repeat of the problem.

The stadium was no match for the storm that struck Friday night.

"This has got to be one of the worst environments I've ever been in as a player," Mississippi State's Charles Rhodes said. "To see stuff falling from the roof, it really scared me. I really didn't know what to do."

AP freelance writer Amy Jinkner-Lloyd contributed to this report.