The National Hurricane Centre said the eye of Hurricane Harvey made landfall at about 10pm local time on Friday, about 30 miles north east of Corpus Christi between Port Aransas and Port O'Connor, bringing with it 130mph sustained winds and rain.
The U.S city of Rockport in Texas has bared the brunt of the Category 4 storm.
Aside from storm surges up to 12 feet, Harvey is expected to drop prodigious amounts of rain - up to three feet. The resulting flooding, one expert said, could be "the depths of which we've never seen".
At least one researcher predicted heavy damage that would linger for months or longer.
University of Miami senior hurricane researcher Brian McNoldy said:"In terms of economic impact, Harvey will probably be on par with Hurricane Katrina."
God's Pit Crew is a Christian crisis response organisation from Virginia. Its volunteers have driven two lorries to Texas filled emergency relief supplies. The group will deliver the items to a church which will then distribute them to victims.
U.S Evangelist Franklin Graham has asked for prayers for Texan residents and also said the humanitarian aid organisation he leads, Samaritan's Purse, will participate in clean-up efforts after the storm.
Gateway Church in Southlake, Texas has organised relief efforts with local churches and first responders. It's also has asked for prayers that the storm will weaken, and for residents who are evacuating and in the path of the hurricane.
We are working with local organizations as Hurricane Harvey progresses. Updates will be posted here: https://t.co/FXJZle2pOd
— Gateway Church (@GatewayPeople) August 25, 2017
Tens of thousands of people in Texas have been ordered to take cover from the storm that is expected to impact 6 million people. The last storm of its kind to strike Texas was in 1961.
President Trump has already signed a disaster declaration to get aid to the region.
Texas governor Greg Abbott warned that the monster system would be "a very major disaster" and the predictions drew fearful comparisons to Hurricane Katrina, one of the deadliest to strike the US.
Dennis Feltgen, a spokesman and meteorologist for the National Hurricane Centre said:"We know that we've got millions of people who are going to feel the impact of this storm."
"We really pray that people are listening to their emergency managers and get out of harm's way."
