With maximum sustained winds diminishing to near 110 kph, Lane was forecast to make its nearest approach to land just west of the island chain over the weekend, bringing tropical storm conditions to Maui and the state's most populous island, Oahu, starting on Friday night.

Farther north, a tropical storm watch was posted for the island of Kauai.

The biggest immediate danger was posed by flooding and mudslides that could worsen the longer the storm lingers close to the US Pacific island chain, soaking the landscape.

"We do anticipate lots of rain from Lane in the coming hours," Governor David Ige said at an evening news briefing on Saturday.

A number of structures on the island of Hawaii, popularly known as the Big Island, were destroyed and some residents were reported to be fleeing homes, said Melissa Dye from Weather Service in Honolulu.

Fire crews rescued several people stranded by high water on the Big Island since Thursday, mostly around its biggest city, Hilo, said Hawaii County spokeswoman Kelly Wooten.

She said two Hilo-area neighbourhoods were evacuated without injury.

"I've never seen this, so much devastation of the river flowing down off of Komohana (River)," said longtime resident Tracy Pacheco in Hilo. "I just came from Pahale Park and there's no park."

Official bulletins grew less dire through the day and into the evening, forecasts made clear Hawaii had been spared from the threat of its first direct hit by a major hurricane in a quarter of a century.

Lane was downgraded on Friday to a Category 1, the lowest ranking on the five-step Saffir-Simpson scale, as it churned through the Pacific south of Oahu, the National Weather Service said.

It was downgraded again to a tropical storm shortly before 5 pm as its maximum sustained wind speeds fell below 120km/h.

The storm was nearly stationary south of Hawaii on Friday night.

It was expected to move slowly toward the northwest later and then turn west on Saturday and continue over the weekend, the National Weather Service said.

Forecasts called for Lane, which peaked as a Category 5 hurricane with top sustained winds of 260 kph earlier in the week, to diminish into a tropical depression by early on Sunday.

The turn of events was welcomed by residents who had spent much of the past few days stocking up on food, water, petrol and batteries and boarding up windows.

Australian Associated Press