Hurricane Lane is churning slowly towards Hawaii as schools, government offices and business close and residents stock up on supplies and boarded up homes.
A direct hit could bring the US Pacific island state's worst storm in a quarter century, forecasters said.
A state of emergency has been declared, as winds of up to 230km/h and up to 50cm of rain is predicted lash the islands. Flash floods and landslides are also likely, the National Weather Service said.
To the north, Oahu was under a hurricane warning while Kauai remained on hurricane watch meaning it could face similar conditions starting Friday morning.
Governor David Ige urged residents to prepare for the worst by setting aside a 14-day supply of water, food and medicines.
He also announced that all public schools, University of Hawaii campuses and non-essential government offices on the islands of Oahu and Kauai would be closed for at least two days starting on Thursday.
The shelves of a downtown Honolulu Walmart were stripped of items ranging from canned tuna to dog food. Shoppers jostled with one another to get the last boxes of ramen noodles.
City residents used carts to push cases of bottled water and coolers full of ice, after warnings of possible power outages and evacuations.
Cars waited in long lines at petrol stations in Honolulu and people could be seen pulling small boats from the water ahead of Lane's expected storm surge.
As of 7pm (AEST) the storm was centred 380 km south-southwest of Kailua-Kona, the weather service said.