Schools and offices are closed in Hawaii and residents are hunkering down to ride out the storm as Hurricane Lane spins toward the islands, causing flash floods, landslides and heavy surf.

Key points: Footage on social media shows major flooding

Footage on social media shows major flooding Predictions show waves could reach six metres

Predictions show waves could reach six metres Two campers are reportedly trapped on northern coast, with rescue teams blocked by floods

With the hurricane churning in the Pacific Ocean more than 300 kilometres south-southeast of Kailua-Kona, more than 30 centimetres of rain had already fallen on the eastern side of the Big Island, said Hawaii County Civil Defence agency spokeswoman Kelly Wooten.

There were no immediate reports of injuries, but at least 14 roads had been closed due to flash floods and landslides, she said.

Tourists were advised to stay away from a popular attraction on the island of Maui called the Seven Sacred Pools, a scenic cluster of waterfalls and grottos.

At least 14 roads have been closed due to flooding and landslides. ( AP: Hollyn Johnson/Hawaii Tribune-Herald )

Moving north west at 11kph, the National Weather Service downgraded the storm to a category 3 on the five-step Saffir-Simpson scale.

The storm is packing sustained winds of 209kph.

"Some [further] weakening is forecast during the next 48 hours but Lane is expected to remain a hurricane as it draws closer to the islands," the weather service said in an advisory.

President Donald Trump declared a state of emergency for Hawaii and ordered federal authorities to help supplement state and local responses, the White House said.

The Coast Guard has ordered all harbours to close to incoming vessels and the US Navy moved most of its fleet out of Pearl Harbor, where ships could provide aid after the storm.

Loading...

The latest predictions showed the eye of the storm carving just west of the islands on Friday (local time) before turning back out to sea, but forecasters warned that the island could still expect to be hit hard by the erratic hurricane.

"We're telling everybody to take the storm seriously, make your final preparations, and be prepared to ride out what is going to be a prolonged rain event," said spokesman for the city and county of Honolulu, Andrew Pereira.

The National Hurricane Centre warned that storm surges could bring 6 metre waves and raise water levels 1 to 1.5 metres above normal along the western shores of the Big Island.

Extreme rainfall may prompt "numerous evacuations and rescues", it said.

Pablo Akira Beimler, who lives on the coast in Honokaa on the Big Island, said the road to Hilo was cut off due to landslides.

"Rain has been nonstop for the last half hour or so and winds are just starting to pick up," Mr Beimler said as he posted videos of trees being blown sideways.

"Our usually quiet stream is raging right now."

He said staying put is about the only choice he has.

Surf is predicted to rise to around 6 metres as the hurricane nears. ( AP: John Locher )

Emergency workers rescued five people from a flooded house in Hilo after a nearby gulch overflowed, said Hawaii County managing director Wil Okabe.

They weren't injured and were taken to a shelter, he said.

Two campers were reported trapped overnight in Waipio Valley, along the Big Island's northern coast.

The campers called authorities, but emergency crews could not mount a rescue operation.

"We can't go in because the roads — there's a river of water down there," Mr Okabe said.

Hawaiian residents are purchasing supplies including bottled water, food and toilet rolls. ( AP: Dennis Fujimoto/The Garden Island )

In addition, there were reports of boulders falling into a park in Hilo on the east side of the island, Mr Okabe said.

Loading...

Shelters opened on Wednesday on the Big Island and on the islands of Maui, Molokai and Lanai.

Officials urged those needing the Molokai shelter to get there soon because of concerns that the main highway on the island's south coast could become impassable.

Aid agencies were also working to help Hawaii's sizeable homeless population, many of whom live near beaches and streams that could flood.

Because there are not enough shelters across the state, Hawaii emergency management agency spokesman Tom Travis urged people who were not in flood zones to stay home.

Governor David Ige urged residents to prepare for the worst by setting aside enough water, food and medicines for 14 days.

All public schools, University of Hawaii campuses and non-essential government offices on the islands of Oahu and Kauai will be closed for at least two days from Thursday, he said.

The most powerful hurricane on record to hit Hawaii was the category 4 Iniki, which made landfall on Kauai island on September 11, 1992, according to the National Oceanic and Atmospheric Administration.

It killed six people and damaged or destroyed more than 14,000 homes.

Lane comes as people on Big Island continue to deal with ongoing eruptions from the Kilauea volcano.

AP/Reuters