"We're riding every line to assess the extent of the damage and working closely with the city and county to safely bring power back to our customers in the Pine Belt", Michael Harvey said.
He said it was too soon to estimate the number of injured people.
As of 3 p.m., a storm team of almost 300 is working to restore power to approximately 4,000 customers in the Hattiesburg and Petal areas. The city also said that firefighters and police are going door-to-door to try to rescue victims.
Photos and television images showed the intensity of the damage.
The Mississippi Emergency Management Agency said it had received reports of "extensive damage" in three counties - Forrest, Lamar and Perry - in the area of Hattiesburg, Miss.
William Carey Campus. Source WDAM
Some people remain trapped in their houses, said Forrest County Emergency Management Director Glen Moore.
In the aftermath of the storm, people were trapped in their homes and Mayor Johnny DuPree issued an emergency declaration and told reporters that a search and rescue mission is underway in the city of more than 48,000 citizens. More rain - one to two inches - is possible.
The Mississippi Highway Patrol reported that Interstate 59 north of Hattiesburg was closed due to debris and most roads in Petal were deemed impassible.
Officials warned of downed power lines and debris spread over large areas and urged people to avoid traveling.
Flynn said the tornado touched down in Lamar, plowed through Forrest and then struck Perry before dissipating.
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