Cars and trucks streamed inland and chemical companies buttoned up their plants yesterday as Hurricane Ike took aim at the heart of the U.S. refining industry and threatened to send a wall of water crashing toward Houston.

Ike's gargantuan size -- not its strength -- will likely push an extra-large storm surge inland in a region already prone to it, experts said yesterday.

Ike's giant girth means more water piling up longer on Texas and Louisiana coastal areas, topped with bigger waves. Its storm surge -- the prime killer in hurricanes -- will be far worse than typical for a storm of Ike's strength, the National Hurricane Center said.

A 1900 hurricane following a similar track to Ike inundated Galveston Island, killing more than 6,000 people.

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Nearly 1 million people along the Texas coast were ordered to evacuate ahead of the storm, which was expected to strike late today or early tomorrow. But in a calculated risk aimed at avoiding total gridlock, authorities told most people to just hunker down.

The National Hurricane Center is forecasting a 20-foot surge for a large swath of Texas and the Louisiana coasts. Above that, the center predicts "large and dangerous battering waves." Waves could be 50 feet tall, said hurricane center spokesman and meteorologist Dennis Feltgen.

"It's going to do tremendous damage over a large area even if it doesn't strengthen any more," predicted former hurricane center director Max Mayfield.

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Experts are trying to figure out when they've seen a storm this wide. Ike's tropical storm force winds stretch for 510 miles, and weather radar from Galveston to Key West can see its outer bands. That's about 70 percent larger than an average hurricane.

Ike was steering almost directly for Houston, where the nation's biggest refinery and NASA's Johnson Space Center lie in areas vulnerable to wind and floodwaters. Forecasters said the storm was likely to come ashore as a Category 3, with winds up to 130 mph.

NASA closed the Johnson Space Center, including Mission Control, and set up temporary quarters yesterday near Austin and Huntsville, Ala., to watch over the International Space Station until the storm threat passes.

"It's a big storm," Texas Gov. Rick Perry said. "I cannot overemphasize the danger that is facing us. It's going to do some substantial damage. . . . It's going to cause massive flooding."

Hurricane warnings were in effect over a 400-mile stretch of coastline from south of Corpus Christi to Morgan City, La. Tropical storm warnings extended south almost to the Mexican border and east to the Mississippi-Alabama line, including New Orleans.

Authorities hoped to avoid the panic of three years ago, when evacuations ordered in advance of Hurricane Rita caused a monumental traffic jam. The evacuation proved deadlier than the storm itself. A total of 110 people died during the exodus, including 23 nursing home patients whose bus burst into flames while stuck in traffic.