Texas Governor Greg Abbott on Friday asked President Donald Trump to issue a "major disaster declaration" for the state, as Hurricane Harvey threatens to inflict some of the worst storm damage in a decade.

With the powerful storm just hours from slamming full-force into Texas's Gulf coast, Abbott warned that Harvey was "turning into a very complex and dangerous hurricane."

"We can obviously tell already at this stage this is going to be a very major disaster," he said.

Abbott told reporters he had requested "moments ago" that Trump make the disaster declaration in order to "trigger additional help and assistance from the federal government."