(CNN) -- People along the Texas coast were leaving home or planning to evacuate Thursday as Hurricane Ike churned toward them, slowly intensifying on its march west.



Forecasters say the storm could slam into the Texas coast -- south of Galveston -- as a powerful Category 3 storm late Friday or early Saturday.



Mandatory and voluntary evacuations were planned or underway in at least seven coastal counties.



Aransas County, on the eastern coast of Texas, has ordered a mandatory evacuation of all nonessential government employees, becoming the latest county in the state to urge residents to flee.



In Galveston, city officials ordered mandatory evacuations for part of the island town beginning at 7 a.m. Thursday. The rest of the town will be under a voluntary evacuation order. Only residents will be required to evacuate on the western end of the island.



Mayor Lyda Ann Thomas defended that, saying current models call for Galveston to be hit with winds and rain only equivalent to a Category 1 hurricane.



"We do not intend to evacuate Galveston Island," she said. "It's the last thing we want to do. Our job is to protect lives and property, [and] right now we feel that sheltering in place is the best action for our citizens to take."



Farther up the Gulf Coast and closer to where the National Hurricane Center predicts a direct hit, Brazoria County ordered a mandatory evacuation to begin at 8 a.m. Thursday. Some other Texas localities have ordered mandatory evacuations, while others have left the decision to depart up to residents.



As of 5 a.m. ET Thursday, the Category 2 storm -- with top sustained winds near 100 mph -- was about  620 miles east of Brownsville, Texas, and about 285 miles southeast of the Mississippi River, the hurricane center said. Track the storm »



Hurricane-force winds extended out up to 115 miles from the storm's center, and tropical storm-force winds extended out up to 255 miles forecasters reported.



About 15,000 residents were leaving Galveston's Brazoria County Wednesday after a mandatory evacuation order was issued at 10 a.m. CT (11 a.m. ET) governing one ZIP code -- 77541 -- and residents throughout the county with special needs.



Galveston City Manager Steve LeBlanc issued a warning to residents of the city's West End, citing forecasters' estimates that the area could get tides of 6 feet above normal if the storm arrives there. The West End is the area of Galveston most susceptible to flooding, LeBlanc said.



Other Brazoria residents were being allowed to remain as of 6 p.m. ET.



In Matagorda County, southwest of Galveston, officials ordered a mandatory evacuation for all areas except the cities of Bay City and Van Vleck.



The evacuation must be completed by at 6 p.m. (7 p.m. ET) Thursday. Galveston is likely to experience a high tidal surge, officials said, urging people living in low-lying areas or mobile homes to get out soon.



"One of the things that the public has to understand if they decide to stay, there will be a period of time during this storm when they will absolutely be on their own," Brazoria County Sheriff Charles Wagner said.



"There will be no medical services; there will be no fire department; there will be no law enforcement, groceries, gasoline, drugs, electricity."



The center issued a tropical storm warning from the Mississippi River's mouth to Cameron, Louisiana, and a hurricane watch from Cameron to Port Mansfield, Texas, about 60 miles south of Brownsville. Tropical storm warnings mean winds of 39 to 73 mph (63 to 118 kmh) are expected within a day, and a hurricane watch means winds of 74 and higher are expected within 36 hours.



"Hurricane Ike is now in the Gulf of Mexico and making its approach toward our coast," Gov. Rick Perry said in a statement. "The next few days will be crucial for residents to follow the direction of local leaders and to take the necessary steps to protect themselves and their families."



Perry put 7,500 National Guard members on standby this week, his office said, and issued a disaster declaration
What category could the tornado swell to? When is Ike expected to hit the Texas coast? Mandatory evacuations are ordered for which residents of one county? What category storm could Ike swell to when it hits Texas on Saturday? What is the name of the hurricane? Who was mandated to evacuate? What is the name of the tornado?
3 late Friday or early Saturday. Aransas 3 Ike residents Ike
question: What category could the tornado swell to?, answer: 3 | question: When is Ike expected to hit the Texas coast?, answer: late Friday or early Saturday. | question: Mandatory evacuations are ordered for which residents of one county?, answer: Aransas | question: What category storm could Ike swell to when it hits Texas on Saturday?, answer: 3 | question: What is the name of the hurricane?, answer: Ike | question: Who was mandated to evacuate?, answer: residents | question: What is the name of the tornado?, answer: Ike