Molten lava from a volcano in Hawaii is pushing closer to a rural area, closing the main road and triggering warnings that residents might need to leave their homes at any time.

Dozens of people in the path of the flow were told to prepare for a possible evacuation, Hawaii County Civil Defense said in an advisory Sunday night. No evacuations had yet been ordered.

The Red Cross said it was opening a shelter to aid any evacuees.

Authorities said late Sunday that lava flow on the Big Island of Hawaii had picked up speed, advancing about 170 yards since 9 a.m. and moving at a rate of about 15 to 20 yards an hour.

The flow that has been threatening Pahoa, the largest town in the mostly rural region of Puna on the Big Island, began in June. It's been moving toward town in fits and starts for weeks, speeding up and then slowing down.

The flow came within less than a half-mile of Pahoa Village Road, the main street of Pahoa, leading officials to close it to all but local residents. The flow front also passed through a predominantly Buddhist cemetery, covering grave sites.

Darryl Oliveira, director of civil defense for Hawaii County, told reporters during a Sunday morning teleconference that the nearest home was at least 300 yards from the flow front.

Residents in the nearest home said they could see the flow front from their balcony and were prepared to evacuate when the time came, Oliveira said. He estimated there were at least 50 to 60 structures, including homes and businesses, in the area most likely to be impacted.

Authorities went door to door notifying residents to be ready to evacuate. Most residents had identified places where they could go, with "less than a handful" saying they may need to go to a shelter, Oliveira said.

The flow stems from the Kilauea volcano, which has been erupting continuously since 1983. Most lava from this eruption has flowed south, while the lava has flowed to the northeast over the past two years.

Janet Babb, a geologist and spokeswoman for the Hawaiian Volcano Observatory, said methane explosions also have been going off. She said decomposing vegetation produces methane gas that can travel below the Earth's surface beyond the lava front in different directions, accumulating in pockets that can ignite. She said it was a bit unnerving to hear all the blasts on Saturday.

One passed near where she and others were standing.

"At the time that it happened, it was such a rumble I thought it was thunder and that we were about to be struck by lightning," she said.