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.

Diana Acevedo said she and her family considered leaving their double-wide trailer, but they had called around and it was too late to find a place to stay. Looking out at a rickety swingset and tricycle in the front yard, Acevedo said they would pick up loose items today and perhaps board windows like some of her neighbors.

“I think it’s going to get really bad,” she said. In previous heavy rains, water filled with sewage from flooded septic tanks has lapped near her door, more than two feet off the ground.

Galveston Mayor Lyda Ann Thomas extended a mandatory evacuation that had covered the west side of the island, unprotected by a seawall, to the entire island.

She said the city, virtually destroyed by a hurricane in 1900 that killed more than 6,000 people and remains the nation’s worst natural disaster, will not open shelters. She advised those who chose to ignore the order to have supplies like food, water and medicine and secure their homes.

“This is a very hard call for me to make but our intent is to save lives,” she said. “We believe it is best for people to leave.”

In Louisiana, where Labor Day’s Hurricane Gustav was blamed for 29 deaths, officials closed flood gates and state offices along the coast.

“Today would be a good time for folks to fuel up their cars, just to make sure they have sufficient supplies,” Gov. Bobby Jindal said, adding the state corrections department had evacuated about 1,400 prisoners from Cameron and Calcasieu parishes in the state’s southwest.

Ike was a Category 2 storm as of 2 p.m. EDT Thursday with top sustained winds near 100 mph, the National Hurricane Center said. It was over the Gulf’s energizing warm waters about 440 miles east-southeast of Corpus Christi and moving west-northwest near 10 mph after ravaging homes in Cuba and killing dozens of people in the Caribbean.

The Port of Houston, the nation’s second largest port, planned to shut down operations Thursday afternoon and remain closed until Monday.

The oil and gas industry also watched the storm closely, fearing damage to the very heart of its operations.

Refineries on the upper Texas coast account for one-fifth of U.S. refining capacity. Exxon Mobil Corp.’s plant in Baytown, outside Houston, is the nation’s largest refinery. Exxon Mobil, Valero Energy Corp., ConocoPhillips and Marathon Oil Co. were among the companies halting operations as the storm closed in.

Refineries are built to withstand high winds, but flooding can disrupt operations and — as happened in Louisiana after Hurricane Gustav — power outages can shut down equipment for days or weeks.

Supply concerns sent wholesale gasoline prices soaring to record levels between $4 and $5 a gallon Thursday. That means retailers will pay more for gasoline, and consumers can expect hikes at the pump. How much gas prices rise, analysts say, depends largely on how long refineries remain shuttered after the storm passes.

Dow Chemical Co. was shutting down its enormous Freeport facility, home to 75 plants producing some 27 billion pounds of chemical or chemical products each year, and its 139-acre LaPorte site, said Dow spokesman David Winder.

In the Florida Panhandle, Ike pushed up storm surge that flooded a highway on Okaloosa Island as the storm passed in the Gulf. U.S. Highway 98 was closed, and was expected to stay closed through Saturday. The Panhandle, where surf was up to 5 feet higher than usual in some places, also was under a high surf warning, and emergency officials urged beach-goers to stay out of the rough water.