(CNN) -- A tornado touched down in southern Mississippi on Sunday, injuring more than a dozen people and causing widespread damage.

So far, no one has been reported killed, which authorities hope will remain true.

"We're really blessed because we don't have a fatality that we know of right now, and no major injuries. But we have a number of major damages to our structures around town," said Johnny DuPree, mayor of Hattiesburg, where the tornado hit.

"If there is a good thing about this, it happened on a Sunday when most of these structures were vacant," he said.

Mississippi Gov. Phil Bryant declared a state of emergency in four counties: Forrest, Lamar, Lawrence and Marion.

Hattiesburg, which straddles Forrest and Lamar counties, is home to the University of Southern Mississippi. It suffered damage to several buildings, but there were no reports of injuries there. University police declared a state of emergency and urged those not on campus to stay away until further notice.

Nearby Oak Grove High School also suffered damage. Randy Wright posted photographs to his Twitter account of the school, showing debris strewn on what looked to be a parking lot and a truck upside down in a baseball diamond.

The Hattiesburg Public School District canceled classes Monday. The university campus will also be closed.

"There's quite a few homes without power at this point. Quite a few trees on houses, on cars, that type of thing," said Forrest County Sheriff Billy McGee.

He said that from 10 to 15 people were taken to the hospital, but that none suffered serious injuries. Another three were reported injured in nearby Marion County.

It was not clear how those people were hurt.

Sarah Lawrence, a Hattiesburg resident, said that the storm sounded like "stuff being thrown."

"Within seconds, everything changed," she said. "I didn't feel like there was much notice. I heard the sirens and everything looked OK outside, so I started making preparations to go into the bathroom. And then, next thing I know, all the lights went out, and it got dark outside."

As the storm system moved east Sunday night, tornado warnings were issued -- then expired -- for parts of southeastern Mississippi and southwestern Alabama.

CNN's Maggie Schneider, Elwyn Lopez and Janet DiGiacomo contributed to this report.

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