Harvey came ashore on Friday night northeast of Corpus Christi, Tex., making landfall as a Category 4 hurricane with 130-mile-per-hour winds.
According to AAA, almost half of US refineries are on the Gulf Coast, and a third of them are in Hurricane Harvey's path. Portland, Rockport, Port Aransas, Aransas Pass, Ingleside and Robstown have also been issued evacuation orders.
So far, there have been 338,000 power outages across the state, he added.
Rockport City Manager Kevin Carruth said by phone that he had heard reports of a tree falling into a mobile home and roofs collapsing on houses. "But we will be getting out here before too much longer and trying to see what we got left".
This means areas that were already hit hard along the Texas coast should expect even more rain and wind, setting the stage for potentially catastrophic flooding and storm surge.
President Donald Trump, facing the first large-scale natural disaster of his presidency, granted Texas Governor Greg Abbott's request to declare a "major disaster" zone in the state to speed federal aid to the millions in harm's way.
Some areas could get up to 40 inches (more than 100 centimeters) of rain, according to the NHC, which warned of "extremely serious flooding", while some communities were hit by localised tornados.
"The storm surge, coupled with the deluge of rain, could easily lead to billions of dollars of property damage and nearly certainly loss of life", Texas Governor Greg Abbott wrote to Trump in request of a disaster proclamation.
Four refineries in South Texas have shut down, disrupting gasoline supplies and pushing prices higher. With more and more shelters opening up as the storm moves inland, there's bound to be one nearby.
"We are leaving nothing to chance". The town of Rockport has about 100,000 residents.
Its size and strength also dredged up memories of Katrina, the 2005 hurricane that made a direct hit on New Orleans as a Category 3 storm, causing levees and flood walls to fail in dozens of places.
The region is facing the prospect of catastrophic flooding from the torrential rains. In Texas, 1,915 homes were destroyed.
Texas is vital to American oil production, with the Gulf Coast responsible for almost a quarter of total US crude oil production and almost half of total USA petroleum refining capacity, reports CNN Money.
Twenty-five members of the Central Florida Urban Search and Rescue Task Force 4 team are on standby to deploy to help with hurricane rescue efforts should they be called, Orlando Fire Department spokeswoman Ashley Papagni said.