HONOLULU -- Hawaii authorities on Saturday told several dozen residents near an active lava flow to prepare for a possible evacuation in the next three to five days as molten rock oozed across a country road and edged closer to homes.

The flow is currently about 160 to 230 feet wide and moving northeast at about 10 yards per hour.

The lava crossed a road on the edge of Pahoa, the largest town in the mostly rural region of Puna on the Big Island of Hawaii, at 3:50 a.m.

It's currently about six-tenths of a mile from Pahoa Village Road, the town's main street.

It's not clear when it might reach the village road as the flow has been advancing erratically, said Matt Patrick, a geologist with the Hawaiian Volcano Observatory.

Officials were going door-to door to about 50 homes to keep residents informed of the lava's movement, said Darryl Oliveira, the director of civil defence for Hawaii County.

"This is all something we've been preparing for and hoping wouldn't have to happen," Oliveira said.

The county will issue a mandatory evacuation order if the flow begins advancing at such a rate that it would be difficult for people to move out of the way with little notice, Oliveira said.

The presence of hazardous materials -- like a pile of tires or a stockpile of chemicals -- in the flow's path would also trigger a mandatory evacuation order, he said.

Burning asphalt was generating some smoke, but Oliveira said the wind dispersed the fumes over unpopulated areas and it didn't pose a health risk at the moment.

Kilauea volcano has been erupting continuously since 1983. Most lava from this eruption has flowed south. But the lava has flowed to the northeast over the past two years.

The current flow that has been threatening Pahoa began in June. It's been moving fitfully toward the town for weeks, speeding up and then slowing down.

Sporadic suspensions in the lava's movement gave emergency crews time to work on building alternate routes to town in the event the flow covers the main road and highway.

Crews near the leading edge have been wrapping power poles with concrete rings as a layer of protection from the lava's heat.

The lava's pace picked up in recent days when it reached a gully, allowing it to move more efficiently like rain in a gutter.

Hawaii Gov. Neil Abercrombie on Friday asked for a presidential disaster declaration to get federal help for local emergency crews.