PHOTO GALLERY: PAHOA PREPARES

Concerns over a river of lava that destroyed a farm shed Tuesday morning kicked into another gear later in the day as lava ignited a stockpile of tires, sending black smoke into the sky, and Civil Defense officials prepared to issue qualified evacuation orders by sundown.

The first of four newly insulated power poles on Apaa Street — which already has been overrun by lava — appeared to be succumbing to the 2,100-degree heat. And a two-story home, a warehouse and farmer’s house on an anthurium farm near the lava flow remained in danger Tuesday afternoon.

Dozens of unarmed soldiers from the Hawaii Air and Army National Guard were to begin patrolling the streets of Pahoa Wednesday as officials prepared for an onslaught of traffic and tourists.

Hawaii County police also were moving out of their sub-station into temporary headquarters on Pohiki Road in Pahoa, said Hawaii County Civil Defense administrator Darryl Oliveira.

The lava had only advanced 20 yards by 11:30 a.m. but suddenly gained new speed and traveled another 100 yards by 3 p.m. threatening a two-story rental home, a warehouse and farm house on a contractor’s anthurium farm, Oliveira said. 

Between the anthurium farm and Pahoa Village Road — about five football fields away — lie another six to 12 homes, businesses and a bed-and-breakfast that are also at risk, Oliveira said.

"It’s unlikely we’ll need to issue a mandatory evacuation, but we’re prepared to do that," he said.

Police, fire and Civil Defense officials plan to once again go door-to-door Tuesday afternoon to warn residents of the dangers. But the decision to leave will be up to each person, Oliveira repeated.

Allowing people to remain would be "part of the overall grieving process" in losing a home, he said.

The two-story rental home on the anthurium farm early Tuesday lied directly in the path of the lava, which then took a turn and burned down a 10-foot-by-15-foot utility potting shed, Oliveira said. 

It was the first structure to be destroyed by the lava from Kilauea Volcano, which began June 27.

Later Tuesday, the lava then ignited a stack of tires on the farm, Oliveira said.

Concerns over the lava flow increased when it crossed Apaa Street over the weekend. But the destruction of the shed is "definitely going to change the dynamics," Oliveira said.

Oliveira continued to debunk unsourced reports of looting.

The flow is expected to cross Pahoa Village Road somewhere between Apaa Street and Post Office Road.

Geologists said the flow stopped advancing between 2 a.m. and 5 a.m., while it filled a low point in the ground. At 6 a.m., the leading edge of the flow was about 82 yards wide and moving to the northeast.

The lava was about 70 yards from the nearest home Monday night.

Hawaii County Civil Defense planned to allow those living in the path of a lava flow to watch the destruction of their homes.

That accommodation is being made to "provide for a means of closure," Hawaii County Civil Defense Director Darryl Oliveira said Monday. "You can only imagine the frustration as well as … despair they’re going through."

The flow advanced about 275 yards from Sunday morning to Monday morning, moving northeast at about 10 to 15 yards per hour. At other times, the lava slowed to about 2 yards an hour or sped up to about 20 yards an hour, depending on topography, said Janet Babb, a spokeswoman for the Hawaiian Volcano Observatory.

Teams of scientists from the observatory were walking alongside the flow day and night to provide updates, she said.

Officials closed part of Pahoa Village Road to everyone except residents as the flow front moves closer.

Those living downslope of the flow are under an evacuation advisory. Most residents have left, and Oliveira said he doesn’t anticipate having to issue a mandatory evacuation order.

Residents have had weeks to prepare for what’s been described as a slow-motion disaster. Most have either already left or are prepared to go when necessary.

The couple living in the house closest to the flow have left but have been returning periodically to gather belongings, Oliveira said.

Apaa Street resident Imelda Raras said she and her husband are ready to go to a friend’s home if officials tell them they should leave.

"We are still praying," she said. "I hope our home will be spared."

Scientists began warning the public about the lava on Aug. 22. At the time, residents were cleaning up from a tropical storm that made landfall over the Puna district.

The lava has advanced and slowed as residents waited and watched.

Kilauea volcano, one of the world’s most active, has been erupting continuously since 1983.

Decomposition of vegetation in the lava’s path has created methane gas, which if it accumulates and is ignited by heat can cause a blast, Babb said.

"It’s not a massive explosion," she said. "But it can dislodge rocks. It can hurl large rocks several feet."

In the 1990s, about 200 homes were destroyed by lava flows from Kilauea.

The last evacuations from the volcano came in 2011. One home was destroyed and others were threatened before the lava changed course.

The lava isn’t a reason to cancel a Big Island vacation because it is an isolated event. But officials have warned people to stay away from the area and imposed flight restrictions because of helicopter tours hoping to see lava.

The Associated Press contributed to this report.