( CNN ) -- Emergency officials in seven Mississippi counties were dealing Monday with widespread damage after a swarm of storms swept through the area Sunday evening , injuring scores of people . No deaths have been reported . Two people in Lamar County were critically hurt , the Mississippi Emergency Management Agency said . A tornado struck Hattiesburg , a southern Mississippi city that straddles Lamar and Forrest counties . The Weather Service described the storm as packing 170 mph winds -- an EF-4 on the service 's tornadic scale . The scale ranges from EF0 to EF5 . Hattiesburg Mayor Johnny DuPree reported major damage to a number of buildings . `` If there is a good thing about this , it happened on a Sunday when most of these structures were vacant , '' he said . Tornado sirens were activated 20 to 30 minutes before the twister touched down , DuPree said . `` I think that was enough for people to find shelter , to go to a place in their house that was safe , '' he added . Several homes were destroyed in Marion County , and numerous structures -- including businesses and public buildings -- sustained `` significant damage , '' the state emergency management agency said . As of Monday morning , 4,000 power customers were without electricity , down from the approximately 14,000 who had lost power , Mississippi Power spokesman Mark Davis said . Mississippi Gov . Phil Bryant declared a state of emergency for the affected counties . The declaration means state resources and assets can be used to support local response efforts . Some 63 people were treated at area hospitals , most of them for minor injuries , he said . Some 200 mobile homes were damaged or destroyed , and 100 apartments were damaged and uninhabitable , he said . Bryant tweeted photos of the storm damage . iReporter shopping at Target captures video of tornado . In Hattiesburg , the University of Southern Mississippi suffered damage to several buildings , but there were no reports of injuries there . The campus was already closed because of Mardi Gras and was to remain closed through Tuesday ; classes were canceled through Wednesday . `` We never lost power , '' said Joe Paul , vice president for student affairs , in a statement on the school 's website . `` The cafeteria is up and running , and everyone is fine . '' 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 , showing debris strewn on what appeared to be a parking lot and a truck upside down in a baseball diamond . The Hattiesburg Public School District canceled classes Monday . `` There 's quite a few homes without power at this point , '' Forrest County Sheriff Billy McGee said . `` Quite a few trees on houses , on cars , that type of thing . '' Ten to 15 people were hospitalized , but none suffered serious injuries , he said . It was not clear how those people were hurt . Sarah Lawrence , a Hattiesburg resident , said the storm sounded like `` stuff being thrown . '' `` Within seconds , everything changed , '' she said . `` I did n'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 . '' Northeast begins digging out from major blizzard . The 10 deadliest U.S. tornadoes on record . 23 incredible weather photos . CNN 's Maggie Schneider , Chandler Friedman , Elwyn Lopez and Janet DiGiacomo contributed to this report .
NEW : Hattiesburg tornado was packing 170 mph winds , weather report says . More than a dozen people are injured , including two critically ; no deaths are reported . Mississippi Sen . Phil Bryant declares a state of emergency for affected counties . About 4,000 people are without power , Mississippi Power says .