Honolulu, Hawaii - Tropical Storm Lala on Saturday dumped heavy rain on Hawaii's Big Island, with hurricane-force winds and heavy surf expected.

The governor of the Pacific island state declared a state of emergency as the storm barrelled towards the archipelago, packing winds of 65 miles per hour.

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.

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.

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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.

A hurricane warning was in effect for Hawaii County, which covers the Big Island, and a tropical storm warning was in effect for the islands of Maui, Molokai, and Kahoolawe to its northwest.

"Damaging hurricane-force winds are expected on the Big Island of Hawaii later today," the National Hurricane Center said in its latest advisory. "Tropical storm-force winds are already beginning."

The heavy rainfall "will produce life-threatening flooding and mudslides, especially in areas of steep terrain."

The National Oceanic and Atmospheric Administration (NOAA) said rainfall of up to 25 inches could be seen on the Big Island, and a storm surge of 1-3 feet accompanied by "dangerous waves."

Rough conditions could persist into Sunday.

"It's a serious storm," Governor Josh Green said, proclaiming a state of emergency to ensure the state 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 the area for the storm's impact, and urged residents to be ready.

"I am asking everyone to finish your preparations today," he said. "Don't wait for the weather to deteriorate."

Residents 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.

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

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

El Niño, 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.

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.

"Stay away from beaches and coastal areas where rough surf and rip currents could sweep you away," it added.