Hurricane Harvey has made landfall in Texas after gaining strength and being reclassified as a Category 4 storm shortly before it hit the US southern coast.
It has now been downgraded to a category 1 storm but is it is thought to be the worst to hit the US for 12 years.
There are fears it could create 12-foot storm surges and severe flooding.
President Donald Trump has made an official disaster declaration in response to the hurricane, meaning federal funds and resources will be able to be released quickly to deal with the aftermath.
According to the US National Hurricane Centre the storm made landfall between Port Aransas and Port O'Connor in Texas at 10pm local time bringing with it 130mph winds and torrents of rain.
Immediately after it hit there were warnings of "catastrophic flooding expected due to heavy rainfall and storm surge".
Imagery shared by the National Environmental Satellite showed the scale of the storm as it was came ashore.
Ahead of the hurricane making landfall thousands of people had been evacuated from their homes as Texas authorities declared a state of disaster in the face of the "life-threatening" tropical storm.
Eleven million people were also reported to be under flash food watch, and more than 100,000 without power in Corpus Christi and surrounding areas, as the storm swept across the south.
Forecasters have predicted that the storm could last as long as three days with the possibility of rain totals over several days extending into next week exceeding 24 inches.
Concerns over a threat of flooding brought by tropical downpours have already been raised and residents were warned to prepare for the worst as the governor of Texas warned before the storm hit that it would be "a very major disaster".
At least one researcher has also already predicted there will be heavy damage left in Harvey's wake that could 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.
“The Houston area and Corpus Christi are going to be a mess for a long time.”