Torrential rains struck Hawaii as Hurricane Lane moved toward the island state, triggering landslides and flash flooding.
The National Weather Service said the hurricane was packing winds in excess of 195 kilometers per hour, despite being downgraded to category three.
Currently located some 230 miles south of the capital Honolulu, Hurricane Lane was expected to hit very close to the islands on Thursday night or Friday morning.
"Hurricane Lane is still a dangerous and powerful storm," Governor David Ige told a news conference on Thursday afternoon.
Up to 12 inches of rain had already fallen before dawn, federal authorities said, with 30 inches expected in the worst-hit areas over the coming four to five days.
Over two feet of rain have already fallen at a couple of locations on the windward side of the Big Island, the National Hurricane Center said.
Emergency teams have set up 16 evacuation centers, with a further 19 due to open later as President Donald Trump, who has declared a state of emergency, 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.
Brock Long, chief of the Federal Emergency Management Agency (FEMA), said authorities were "extremely concerned about the potentials for inland flooding, landslides occurring and damage to the transportation, communications infrastructure."
Residents across the state stocked up on water, food, gasoline and emergency supplies as Lane drew nearer.
"Last couple of days it's been like this -- it's been busy," said Chris, an employee at a gas station in Haleiwa, on the north shore of Oahu island -- the location of the capital Honolulu.
"We have been just constantly getting cars filling up. Everybody is in a panic mode right now -- everyone is filling up gas, gas cans, propane cans and all that."
Landslides and flooding caused by the first rainstorm partially blocked several roads on Big Island, according to local media.
Sea levels were expected to rise as much as two to four feet above normal tide levels, causing coastal erosion and prompting a storm surge and "large and destructive waves."
Surfers could be seen taking advantage of the calm before the storm to get out on their boards one last time before the ocean got too violent.
United Airlines said it had canceled all Friday flights to and from Kahului airport on Maui, the second-largest island.
Honolulu authorities said they were planning to activate a three-minute island-wide outdoor siren warning system at 4:00 pm (0200 GMT Friday) to alert the public to the possibility of severe flooding.
Free transport will be available between the capital and Oahu island's evacuation shelters, which had welcomed around 350 people by noon, according to the Maui 24/7 local news portal.
The US Coast Guard said 57,000 US military personnel already stationed in Hawaii were ready to provide logistical and medical support or conduct search and rescue missions operations.
"Hurricane Lane is not a well-behaved hurricane," Ige said in a statement as he declared a state of emergency Tuesday on the Big Island. "I've not seen such dramatic changes in the forecast track as I've seen with this storm.
Hurricanes rarely make landfall in Hawaii and the last major storm to strike the state was nearly three decades ago, when Hurricane Iniki barreled into the island of Kauai, leaving six dead and causing billions of dollars in damage.
Federal officials have been working with Hawaiian utility managers to keep a close eye on the power grid, a major vulnerability in Puerto Rico last year when it was hit by Hurricane Maria, a Category 4 storm.
Hurricane-related deaths in Puerto Rico have been estimated at as many as 4,600 people, largely because prolonged and widespread power outages and washed out roads prevented access to health care, US researchers said.