Houston: Authorities in the Houston area and along the Southeast Texas Gulf Coast ordered hundreds of thousands of people to evacuate Thursday as Ike bore down with hurricane-force winds that stretched across more than 200 miles and could gain even more strength.

Forecasters expected the storm's center to reach land this weekend somewhere between Corpus Christi and Houston, potentially punishing Houston and nearby areas even if they are not hit directly. Hurricane winds stretched up to 115 miles in all directions from Ike's center early Thursday.

Mandatory evacuation orders were issued for tens of thousands of people in low-lying areas in Harris County, where Houston is located.

"They are areas subject to storm surge of up to 15 feet and it very important for people to understand we're not talking about gently rising water but a surge that could come into your home," said Harris County Judge Ed Emmett, the county's chief administrator.

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.

Four counties south and east of Houston had earlier announced mandatory or voluntary evacuations, and authorities began moving weak and chronically ill patients by bus to San Antonio, about 190 miles from Houston. About 1 million people live in the coastal counties between Corpus Christi and Galveston.

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.

Some forecasts say Ike could strengthen to a fearsome Category 4 hurricane with winds of at least 131 mph over the Gulf of Mexico, and emergency officials warned it could drive a storm surge as high as 18 feet.

Ike was a Category 2 storm as of 8 am Thursday with top sustained winds of near 100 mph, the National Hurricane Center in Miami said. It was over the Gulf's energizing warm waters about 575 miles east of Brownsville, Texas, and was moving west-northwest near 10 mph after ravaging homes in Cuba and killing dozens of people in the Caribbean.