A powerful hurricane packing heavy rains and potentially devastating winds was headed toward Hawaii on Wednesday, and US forecasters warned the storm could be the most powerful to hit the Big Island in recorded history.

Hurricane Lane bears 258 kph winds and threatens to drop as much as 50 cm of rain over parts of the islands, the US National Hurricane Center said. It posed a new threat to the island chain of 1.4 million people, which is already coping with the three-month eruption of Kilauea volcano on the Big Island.

Lane was rated a Category 5 storm, the most powerful on the five-step Saffir-Simpson scale of hurricane strength.

The most powerful storm on record hitting Hawaii was the Category 4 Hurricane 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.

On Tuesday, Hawaii residents scrambled to prepare for the storm's arrival. Cars waited in long lines outside gasoline stations in Honolulu and members of canoe clubs pulled their boats from the water.

Hurricane Lane was about 540 km south-southeast of Kailua-Kona, Hawaii, with maximum sustained winds of 257 km/h at 2am Hawaii time (1200 GMT), the NHC said. It was expected to begin a turn toward the northwest of the island later on Wednesday, followed by a turn to the north-northwest on Thursday.

"The centre of Lane will track dangerously close to the islands Thursday through Saturday," the NHC said in a Wednesday advisory. "Regardless of the exact track of the centre, life threatening impacts are likely in some areas as the hurricane makes it's closest approach."

The islands of Maui, Lanai and Moloka'i were all under hurricane and flash flood watches on Wednesday. Hurricane warnings were in effect for Big Island Interior, Big Island North and East, Big Island Summits, Kohala, Kona and South Big Island.