Texans who made it through the first ferocious blasts of Hurricane Harvey have been warned that "catastrophic" flooding and storm surges pose a fresh deadly threat as the storm lingers with one person already losing their life.

Harvey slammed into the Texas coast overnight on Friday with winds of up to 130mph before dropping swiftly from a category four storm to a much less severe category one. It calmed to a tropical storm by Saturday afternoon.

But officials say the worst could be yet to come.

A judge in Texas has confirmed one death caused by the Hurricane in the coastal city of Rockford.

The National Hurricane Centre warned that "catastrophic and life-threatening flooding" was expected across the middle and upper Texas coast.

President Donald Trump has declared an official disaster in the area, with experts saying there is a risk of 12-foot storm surges and severe flooding.

Images from Texas on the first morning after the storm showed trailers tossed on their sides, trees downed and roof slates ripped off by the force of the winds.

No deaths were immediately reported, after a high-profile campaign urging residents in high-risk areas to evacuate.

One of the worst-hit places was Rockport, a city of around 10,000 that was directly in the storm's path.

Its mayor said Harvey hit his coastal community "right on the nose" and left "widespread devastation".

Some buildings were destroyed, while other homes, businesses and schools suffered heavily damage.

Whilst the first dramatic destruction is over, there are more troubles ahead as the storm stalls over the Texas coastline for several days.

The real risk lies not in the intensity of the storm, but its duration.

Harvey is moving at just two miles an hour, and is set to drop as much as three feet of rain on to the coast as it slowly moves on over the next five days.

Some areas are already seeing flooding, with the National Hurricane Centre warning people against driving into standing water.

Forecasters are also predicting that the storm may meander into the Gulf of Mexico waters, pick up strength again and then turn back in fora potential second hit on what may be an already flooded Houston-Galveston area.

Coastal areas could be hit by a double whammy of inland flooding plus storm surges whipped up by the storm coming inland.

Some are predicting that in a worst case scenario the damage could be as bad as Hurricane Katrina which devastated New Orleans.

"I can't remember a storm that made landfall that was both very strong and very slow and not really even moving inland and it stalls along the coast," said University of Miami senior hurricane researcher Brian McNoldy.

"The Houston area and Corpus Christi are going to be a mess for a long time."