US President Donald Trump highlighted Puerto Rico's relatively low death toll compared with "a real catastrophe like Katrina" as he saw for himself the devastation caused by Hurricane Maria.

Donald Trump came face to face with hurricane-ravaged Puerto Rico today after denouncing critics of the federal relief effort as "politically motivated ingrates" who need to step up their own response to the crisis.

A slim majority of Puerto Ricans sought to change their ties with the United States and become the 51st US state in a non-binding referendum that would require final approval from Congress.