Hawaii is facing flash floods that may have swept some homes away after category one Hurricane Lala skirted Big Island, as it continues to grapple with strong winds and torrential rain.

Tens of thousands of properties have been left without power and officials have warned people to prepare for “life-threatening” conditions, including mudslides, as the storm continues moving westward to the south of Hawaii.

Lala gained hurricane strength on Saturday, with wind speeds since peaking at 91mph (147km/h). It could dump up to 35in (89cm) of rain in places.

Hawaii Governor Josh Green said on Saturday that one person had died in a weather-related car accident on Big Island, where many roads have been impacted.

Hawaii County said that as of 01:00 local time (12:00 GMT) on Sunday, two areas on Big Island had been hit by flash flooding, adding “several occupied homes may have been swept off their foundations”.

Mayor Kimo Alameda said the county’s civil defense agency had initiated a search and rescue operation to find people whose homes may have been swept away in the floods.

“What makes this very challenging is that there’s rushing water, there’s debris, there’s boulders on the road, and it’s dark,” he explained.

Videos posted by Hawaii’s Department of Transportation show roads flooded with fast-moving water and blocked with fallen trees.

Green warned residents to brace for “an incredible amount of water”.

“Please be very safe… you do not want to be out on the roads,” he said in a video update on social media.

According to the governor, 190 flights have been postponed.

At Ellison Onizuka Kona International – Big Island’s largest airport – 40% of flights were grounded on Saturday, according to tracker Flightaware. Some 80% of flights were called off at its other main airport, Hilo International.

The most dire forecasts from the National Weather Service (NWS) have been issued for areas within Big Island’s south-east, which came closest to the hurricane’s centre.

“Major rainfall flooding may prompt many evacuations and rescues,” the NWS said, adding that rivers and tributaries “may rapidly overflow their banks in multiple places”.

Nearly 115,000 customers had lost electricity on Hawaii as of Sunday morning local time, according to tracker PowerOutage.

Green said three hospitals had also lost power but had backup generators.

In Maui, some residents have also been left without water supply as of Saturday afternoon.

“Crews responded to the area but were unable to continue their assessment due to inclement weather and multiple downed trees,” a county statement said, adding crews would return once it was safe.

Meteorologist Jennifer Myers, who lives in Hilo, eastern Big Island, said landslides had already cut off some roads, while power lines had been ripped down by falling trees.

“I’m looking at the river right now, and it’s really, really high,” she told the BBC about the view from her apartment of the Wailuku River as it meets Hilo Bay.

“The bay that’s usually blue is like blood red right now because of all the sediment and river water in it.”

The hurricane did not make landfall on Big Island, as had been thought possible, instead coming within 30 miles (48km) of its South Point.

Tropical storm warnings are in effect for all eight of Hawaii’s major islands: Big Island, Maui, Molokai, Kahoolawe, Oahu, Lanai, Kauai and Niihau. Big Island was previously under a hurricane warning.

The National Hurricane Center said: “Damaging winds and heavy rain will persist across the Big Island throughout tonight and spread westwards across the smaller islands on Sunday.”

Residents were repeatedly urged by officials to prepare for the storm early.

Local message boards on Facebook show residents filling bags with sand to protect their homes and inquiring about whether stores remained open in the early hours of Saturday.

Hawaii County’s Civil Defense Agency said public shelters were available in every part on Big Island.

Hurricanes are categorised on a scale of one to five, with a category one storm such as Lala on the lower end of the scale, with minimal damage expected.

Iniki, a powerful category four storm, was the last hurricane to hit Hawaii back in 1992.

It caused six deaths and $3bn in damage after making landfall on the southern coast of Kauai.

This year has seen a strong El Niño – a periodically occurring area of unusually warm surface water – develop in the Pacific, driven in part by climate change.

As hurricanes and typhoons feed off warm sea waters, this spike in ocean temperatures could facilitate a higher number of storms that grow to have a greater intensity.