United States: Hurricane Lane drenched Hawaii Thursday ahead of its arrival in the island state, prompting US President Donald Trump to declare a state of emergency as landslides and flash flooding left roads blocked.

The National Weather Service said Lane -- located about 200 miles (320 kilometers) south of Hawaii -- remained a powerful hurricane, packing winds in excess of 130 miles per hour, although it was downgraded to category three mid-afternoon local time.

The eye was expected to sweep very close to or over the islands, 2,000 miles southwest of the mainland US, sometime later Thursday.

Up to 12 inches (30 centimeters) of rain had already fallen before dawn, according to federal authorities, with 30 inches expected in the worst-hit areas over the coming four to five days.

"Someone once told me it wasn't raining when Noah built the Ark," American Red Cross vice-president Brad Kieserman told a news conference in Washington.  "That means that readiness is important -- readiness to make sure we can fulfill our responsibility and the critical infrastructure lifelines."

Emergency teams have set up 16 evacuation centers, with a further 19 due to open throughout the day, authorities said, as Trump urged Hawaiians to hunker down and prepare for the worst.

"Our teams are closely coordinating with the state and local authorities. You are in our thoughts!" Trump tweeted.