One of the most powerful hurricanes recorded in the north Pacific is forecast to make a direct hit on the US island state of Hawaii, American weather services say.

Hurricane Lane briefly strengthened into a category-5 storm on Tuesday, local time, with winds exceeding 250 km/h, before weakening slightly. It was located about 480 kilometres south-east of Hawaii's Big Island. Alerts cover the Big Island, Maui and other major islands.

Qantas, a major carrier taking tourists from Australia to Hawaii, said "no flights have been affected at this stage", according to a spokesman. "But we will continue to monitor the hurricane's path."

On current forecasts, "the centre of Lane will move dangerously close to or over the main Hawaiian Islands from Thursday through Saturday," the US National Weather Service, said.