Authorities in the Houston area and along the Southeast Texas Gulf Coast ordered hundreds of thousands of people to evacuate Thursday as Hurricane Ike lumbered toward the coast and threatened to grow even stronger.

Traffic was building on roadways leading away from low-lying areas in Galveston County, and officials urged residents to finish storm preparations quickly. Some gas stations were running out of fuel as residents scurried to leave.

“It’s a big storm. I cannot overemphasize the danger that is facing us,” Gov. Rick Perry said at a news conference. “It’s going to do some substantial damage. It’s going to knock out power. It’s going to cause massive flooding.”

Forecasters issued a hurricane warning for the Texas Gulf Coast from the Louisiana state line to near Corpus Christi. The warning, which also extended east along much of the Louisiana coast to Morgan City, means hurricane conditions could reach the coast by late Friday with the front edge of the storm before its powerful center hits land over the weekend.

In Houston, gleaming skyscrapers, the nation’s biggest refinery and NASA’s Johnson Space Center lie in areas that could be vulnerable to wind and floodwaters if Ike crashes ashore as a major hurricane.

Ike is expected to become at least a Category 3 storm, with winds upward of 111 mph, before it comes ashore, the National Hurricane Center in Miami said. Some forecasts indicate Ike could grow to a Category 4, with winds of at least 131 mph. Emergency officials warned it could drive a storm surge as high as 18 feet.

If current projections of the storm’s path hold up, the area surrounding Houston — home to about 4 million people — would be lashed by the eastern or “dirty” side of the storm, said meteorologist Jeff Masters, co-founder of San Francisco-based Weather Underground. This stronger side often has punishing rains, walloping storm surge and tornadoes.

Authorities were hoping to avoid the traffic gridlock of three years ago, when Hurricane Rita threatened the area, and urged people who don’t live in eight specific zip codes in the low-lying areas and near Galveston Bay to remain at home.

“We are still saying: Please shelter in place, or to use the Texas expression, hunker down,” said Harris County Judge Ed Emmett, the county’s chief administrator. “For the vast majority of people who live in our area, stay where you are. The winds will blow and they’ll howl and we’ll get a lot of rain but if you lose power and need to leave, you can do that later.”

Evacuation orders were also issued for all of Jefferson and Orange counties, an area home to more than 320,000 people between Houston and the Louisiana state line, and part of San Patricio County farther south.

In Tierra Grande, a low-lying rural neighborhood, or colonia, south of Corpus Christi, residents struggled with the cost of evacuation and the strong pull to stay with their homes and animals. Few, if any, appeared to be leaving.