There's also the likelihood of catastrophic flooding as the most powerful storm in over a decade to hit the mainland United States.
The hurricane made landfall northeast of Corpus Christi with maximum winds of 130 miles per hour.
The storm is expected to move slowly over the Texas and Louisiana coasts for days, with forecasts for storm surges of up to 13 feet and over 3 feet of rain.
The town of Rockport appeared to be one of the hardest hit by Harvey's punch, hours after the mayor told anyone staying to write their names on their arms for identification in case of death or injury.
A high school, hotel, senior housing complex and other buildings in the town of 10,000 suffered structural damage, according to emergency officials and local media. Some were being used as shelters.
As many as six million people were believed to be in Harvey's path, as is the heart of America's oil refining operations. The storm's impact on refineries has already pushed up gasoline prices while the U.S. Environmental Protection Agency lifted some rules on gasoline to reduce shortages.
Donald Trump, facing the first large-scale natural disaster of his presidency, said on Twitter he signed a disaster proclamation which "unleashes the full force of government help" shortly before Harvey made landfall.
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