Hurricane Lala on Saturday lashed Hawaii's Big Island with heavy rain and strong winds, as forecasters warned of potentially dangerous flooding across the US Pacific island state.

Lala strengthened into a Category 1 hurricane at around 9:00 am local time (1900 GMT), packing winds of up to 75 miles per hour (120 kilometers per hour).

A hurricane warning was in effect for Hawaii County, which covers the Big Island, and a tropical storm warning was in place for the state's seven other major islands: Maui, Molokai, Kahoolawe, Lanai, Oahu, Kauai and Niihau.

Lala was expected to dump 10 to 20 inches (25 to 50 cm) of rain on the Big Island, with totals possibly reaching 25 inches.

"This rainfall will produce life-threatening flooding and mudslides, especially in areas of steep terrain," the US National Hurricane Center said in its 1800 GMT advisory.

A storm surge of one to three feet will be accompanied by "large and dangerous waves," it said. Swells generated by Lala would build through the weekend and are likely to cause "life-threatening surf and rip current conditions."

The rough conditions could persist into Sunday.

"It's a serious storm," Governor Josh Green said, proclaiming a state of emergency to ensure Hawaii and its counties "have sufficient resources to clear debris, secure infrastructure, and take other measures to prepare."

Honolulu Mayor Rick Blangiardi said Friday his administration had spent days preparing for the storm, and urged residents to be ready.

Drivers were seen filling up their vehicles with gasoline.

The state was last hit by a "major" hurricane -- meaning Category 3, 4, or 5 on the Saffir-Simpson scale -- in 1992, when Hurricane Iniki caused at least six deaths and billions of dollars in damage. 

Hawaii was menaced by Hurricane Fausto last month, before the storm weakened and skirted north of the island chain.

El Nino

The storm comes as a powerful El Nino has formed in the central equatorial Pacific Ocean.

Temperatures are already so high that the National Oceanic and Atmosphere Administration now predicts a 69 percent chance of a "historic event that would exceed the strength of previous El Nino events dating back to 1950" when it peaks between October and December.

El Nino, a natural climate pattern when sea surface temperatures in the central and eastern Pacific Ocean become unusually warm, tends to promote hurricane activity in the Pacific while suppressing it in the Atlantic. 

Human-caused climate change can amplify El Nino's impacts because a warmer ocean and atmosphere increase the availability of energy and moisture for extreme weather events, such as heat waves and heavy rainfall.

Hawaii's emergency management agency recommended residents clear gutters and drains and move valuables off the ground, seal gaps in doors and remove tree limbs that threaten their properties.