Update, 11:30 a.m.:

The Parks Highway is open to one-lane traffic with pilot cars.

"Travelers should expect delays and intermittent closures depending on fire activity. The goal of the day is to keep the road open and move vehicles through the area with pilot cars but that is dependent on fire activity," the Alaska Division of Forestry said.

Check with the 511 road status system before traveling, the Department of Transportation and Public Facilities said.

For travelers between Anchorage and Fairbanks, an alternative route via the Richardson and Glenn highways avoids the fire zone.

Update, 10:49 a.m.:

Mara Hill and her friends were driving south on the Parks Highway from a weekend trip to Fairbanks and Chena Monday morning. They saw no obvious signs of fire until they reached roughly Mile 77, where flames were visible from the roadway.

"It was pretty much right up to the trees," Hill said.

Cars were being let through on the Parks Highway one direction at a time. Hill said her group waited 30-40 minutes to get through. The smoke was thick.

"We could see through the smoke, several cars in front of us. But the smell was enough that even with the windows rolled up and air off I found myself breathing through my mouth."

Update: 10:37 a.m.:

Firefighters from the West Lakes Fire Department, in the Big Lake and Meadow Lakes area, responded to a small brush fire at 9:45 a.m. Monday near the powerful Sockeye Fire, according to Mat-Su Emergency Services director Bill Gamble.

The Horseshoe Lake Fire was about 50 feet in diameter and was controlled in about 15 minutes, Gamble said. Gamble did not immediately know the cause of the fire. Gamble said the Horseshoe Lake fire did not use resources from the Sockeye Fire.

Update, 10:18 a.m., Fairbanks:

Alaska Railroad passenger trains left on time Monday morning from Anchorage and Fairbanks. A railroad spokesman said the railroad is not transporting any hazardous materials and that speeds will be reduced through the fire area.

The spokesman said an emergency vehicle will travel well in front of the train.

Update, 10:10 a.m., Houston:

At an shelter for weary evacuees from the wildland fire roaring through the Susitna Valley, the Matanuska-Susitna Borough's emergency manager told Willow residents the soonest they could return to their homes would be Tuesday.

Casey Cook told about 30 people eating biscuits and gravy Monday morning the "hot and fast" fire now has a perimeter of about 18 miles. Some homes have burned, Cook said, but the borough won't have specifics until it completes a door-to-door damage assessment that began Monday morning.

The Alaska State Troopers are "trying to curtail" residents from returning to homes off the Parks Highway, he said.

Smoke dulled the air at Houston Middle School, and evacuees asked if they'd have to move again, after a shelter at Willow Community Center closed Sunday when the fire neared.

No -- at least, not yet, Cook said.

"Right now this is probably the safest place for you folks."

Original story:

Officials were in the Willow area Monday trying to determine the extent of damage from the Sockeye Fire, which scorched a destructive path through the area, while the fire continues burning into a second day, heading south.

Matanuska-Susitna Borough officials were conducting an on-the-ground assessment early Monday to how much damage the fire had caused. Sunday evening the borough estimated that 10 to 15 structures had burned. Officials Monday morning couldn't immediately confirm how many additional structures were destroyed, but expected that number to grow, and hoped to have a new estimate by noon.

An ever-expanding 15-mile evacuation corridor runs along the Parks Highway from north of Willow down to the Nancy Lakes area, with some 1,700 residential structures inside its perimeter, according to an update posted early Monday by the Matanuska-Susitna Borough and Alaska Division of Forestry, which administers the state's firefighting forces.

As of late Sunday evening, the fire estimated at 6,500 acres was burning on both sides of the Parks Highway, running due south. As of midnight, the fire had reached the Crystal Lakes Road subdivision.

The National Weather Service on Sunday issued a red flag warning for the Susitna Valley, meaning high winds and low humidity could lead to dangerous fire weather. The forecast called for north winds from 10 to 25 mph and 12 to 20 percent relative humidity. The warning was in place through Monday.

One firefighter was treated for heat exhaustion.

Some 210 residents signed in overnight at the evacuation centers in Houston, near Talkeetna, and at the North Star Bible Camp on Willow Fishhook Road, according to the update. Shelters are at Houston Middle School at Mile 53 on the Parks Highway and the Upper Susitna Senior Center at Mile 99.

Close to 200 emergency personnel from multiple agencies are responding to the incident, according to the state and borough.

The Parks Highway will be opened as firefighting and public safety allow, officials say. Officials said to expect periodic closures over the next few days and pilot cars guiding traffic through.

A Forestry Division update said the highway was open to limited traffic during the early hours of Monday morning.

The latest report on the Sockeye Fire near Willow is that the Parks Highway is now open. A pilot car is leading cars... Posted by Alaska DNR- Division of Forestry (DOF) on Monday, June 15, 2015

In a tweet Monday morning, Mat-Su Borough officials said Alaska State Troopers were stopping cars to alternate north and southbound traffic at mile 66.5.

AST stopping point for vehicles is at mile 66.5 of the Parks Highway alternating the north and south traffic. MatSuBorough (@MatSuBorough) June 15, 2015

Five "hot shot" crews from the Lower 48 have been ordered for the fire and are expected to arrive Monday. Fire managers expected the fire to calm down overnight but continue to spread before picking up again.

The Federal Aviation Administration issued temporary flight restrictions in the area to accommodate firefighting aircraft.

The fire started Sunday afternoon on West Sockeye Avenue, about 7 miles north of Willow just off the Parks Highway. Authorities say the fire was human-caused. Rumors among evacuees blamed fireworks, but authorities said an investigation continues.

By Sunday evening, with the fire rampaging down the Parks Highway and bearing down on downtown Willow, hundreds of people took to emergency shelters. More found refuge with friends or family. Many left their homes with pets but also horses and sled dogs. Willow is home to scores of competitive and recreation dog mushers. A Facebook group, Sockeye Willow Fire Pet and Home Resource Finder, was established to help evacuees who needed help with animals.

Despite reports that flames overtook Capital Speedway racetrack in Willow, owners there posted updates on social media that no structures were lost. But residents who evacuated their homes now don't know if they still stand. Houston residents posting on social media overnight said they are getting ready to leave as a precaution, in case the fire makes it that far south.

By Monday, a tweet from the National Weather Service in Anchorage noted the Sockeye Fire was already large enough to be detected overnight on nighttime satellite imagery.

#SockeyeFire already big enough to be detected on nighttime satellite imagery. #akwx #akfire #Alaska pic.twitter.com/cAjbpgqioU NWS Anchorage (@NWSAnchorage) June 15, 2015

A voluntary evacuation area extends from Mile 63 to Mile 78 of the Parks Highway. Between that stretch of highway the evacuation area stretches west to the Susitna River and two miles east of the Parks Highway.

The fast-moving fire started at just 2 acres -- two football fields, minus the end zones -- but quickly exploded out of control as it ran, pushed by swirling winds and high temperatures, through stands of black spruce. Response shifted from one state Division of Forestry wildland fire helicopter and an engine to multiple engines and tankers from West Lakes and Central Mat-Su fire departments to multiple initial attack wildland fire crews from around Alaska, including the Pioneer Peak crew based out of Palmer. Planes and helicopters dropped retardant and water. Multiple aircraft were dispatched to the fire to drop retardant and water on the fire.

The Matanuska-Susitna Borough is handling evacuation procedures. Information regarding evacuations is available through the Borough emergency operations center at 907-861-8500.