Harvey is the first Category 4 hurricane to hit the US since Hurricane Charley in 2004, reports CNN.
The storm, after making landfall on Friday night between Port Aransas and Port O’Connor, is pounding the Texas coast and its millions of residents with hurricane-force winds knocking down trees, power poles and signs, and with torrential rain deluging streets.
According to the NHC, the centre of the storm had passed over San Jose Island, bringing with it a dangerous and powerful eye wall.
some areas will see as much as 13 feet of storm surge and large, destructive waves.
Harvey could drop as much as 40 inches of rain in some places, and up to 30 inches in others, by August 30.
The combination of wind and water could leave wide swathes of South Texas “uninhabitable for weeks or months”, the National Weather Service in Houston said.
Earlier on Friday, Texas Governor Greg Abbott declared a state of emergency for 30 counties that lie in the storm’s path, CNN reported.
Abbott also requested additional federal help with a presidential disaster declaration.
President Donald Trump, who will visit the area next week, has signed a disaster declaration for the state.
Residents were urged to evacuate. A mass exodus from the coast caused extensive traffic jams along the state’s highways, while other people boarded up windows and stocked up on food and water ahead of the storm.