9:45 p.m.: See our updated story: Fast-moving wildfire advances on Willow as residents flee

Update, 8:30 p.m.: Evacuees who had already fled a fast-moving fire on the Parks Highway were preparing to move again Sunday night, as the still-growing Sockeye Fire surged toward Willow and a shelter established at the Willow Community Center.

An evacuation was underway from Nancy Lake Parkway to Sockeye Road, where the fire began about seven hours earlier along the Parks Highway. The new evacuation zone stretched for about 10 miles along the highway.

Willow Fire Chief Mahlon Greene was leaving the community center around 8 p.m. to begin evacuating residents along Willow-Fishhook Road, as helicopters buzzed overhead and displaced dogs barked in the lot outside the facility. Those housed at the community center were moving to Houston Middle School.

Authorities have expanded an evacuation notice for the fire, extending from mile 78 of the Parks Highway south to mile 67 at the Nancy Lake Parkway, said Angelina Marsh, a public information officer with the fire's emergency operations center.

Marsh couldn't immediately confirm whether the notice was voluntary or mandatory, but she said it was her understanding that the notice was mandatory.

The Parks Highway will be closed near the fire all night, she said.

"Do not try to go north or south," said Marsh.

Update, 6:15 p.m.: A wildfire that erupted north of Willow Sunday afternoon has now swelled to more than 1,000 acres, officials said.

"At last report at least 20 homes had been evacuated and that number is expected to grow as the fire size increases," the Division of Forestry reported on its Facebook page. Five hotshot crews from the Lower 48 have also been dispatched to help fight the fire.

"...(F)irefighters have switched from an offensive to defensive strategy and are focusing on structure and point protection while aircraft continue to drop retardant and water on the fire," the division said.

The Parks Highway remains closed from Willow-Fishhook Road at Mile 71.2 on the south and at Mile 77 on the north.

About 30 people were taking shelter at the Willow Community Center Sunday evening including Tamara Boeve, who was busy with 30 dogs and eight cats. Many evacuees are staying with friends instead of going to the emergency shelter, Boeve said in an email.

Willow dog musher Justin High posted a message on Facebook at about 5 p.m. saying he and his wife, Iditarod musher Jaimee High, as well as Iditarod veteran DeeDee Jonrowe are evacuating their homes and dog yards in the Sharen Drive area. The Highs lost their home in a fire last winter and were just starting to rebuild.

The fire started to the north of Kashwitna Lake, west of the Parks Highway, but by late afternoon had jumped the highway and was moving south.

Update, 5:30 p.m.: An Alaska Railroad spokesman says all trains running past the wildfire burning near Willow are expected to make it through to Anchorage today. The fire is running parallel to the tracks and a little over a mile away, according to railroad spokesman Tim Sullivan. One more train, the Denali Star, was still inbound from Talkeetna to Anchorage as of 5:30 p.m. The railroad is keeping an eye on the fire and monitoring track in the area as the train approaches, Sullivan said.

"They've been slowing it down because they've been keeping an eye on the fire. It looks like everything is going to make it tonight," he said.

Meanwhile, Alaska State Troopers were again in the area of Fields Road, one of the first evacuation areas, to make sure everyone was cleared out, spokesperson Beth Ipsen said.

The Anchorage Fire Department was also responding with units, according to a post on the department's Facebook page.

"Anchorage Fire Department is responding with a task force of apparatus to the Willow area at the request of the Alaska Division of Forestry to assist with structure protection," department spokesperson John See wrote.

Update, 5 p.m.: The wind-pushed wildfire threatening Willow has destroyed at least one structure and possibly two, Matanuska-Susitna Borough officials have confirmed. The fire had grown to an estimated "500 acres and growing on both sides of the Parks Highway," the Alaska Division of Forestry said.

The head of the fire has crossed Little Willow Creek and is now between the highway and Alaska Railroad tracks on the east side of the highway.

The highway is blocked at Willow-Fishhook Road at Mile 71.2 on the south and at Mile 77 on the north.

A Big Lake kennel and horse ranch at Mile 53 of the Parks Highway is taking evacuated horses and ponies as well as sled dogs and livestock, according to Heather Jewell, horse trainer at Plettner Kennels and Alaska Horse Ranch.

The National Weather Service has issued a red-flag fire weather warning from 5 p.m. until 10 p.m. Monday for strong winds and low humidity in the Susitna Valley, where Willow is located.

Update, 4:45 p.m.: An evacuation notice has been issued for both sides of the Parks Highway south of Sharen Drive to the Willow community as a fast-moving fire continues to develop north of the community.

The Red Cross has established a shelter at the Willow Community Center, located at Mile 67.9 of the highway, according to Beth Bennett, communications officer with the organization. Only a couple of people were there around 4:30 p.m., but she said the facility is set up to accommodate 60 people.

Given the mushing presence in the area, the Red Cross is also allowing petss to be brought to the shelter, provided they have kennels or tie-outs and enough food and water to last for several days. The Red Cross is coordinating with another organization to take in additional animals if too many are showing up at the shelter.

"That's actually topic No. 1 right now, is how do we handle all of the animals," Bennett said.

Update, 3:50 p.m: A fast-moving wildfire north of Willow has swelled to 200 acres, with a 2-mile-long head from Mile 75 to Mile 77 of the Parks Highway, authorities say.

Some structures near the Capitol Speedway are reported to be threatened. The racetrack was being overrun by the fire at 4 p.m., fire officials could be heard saying on an open emergency radio frequency.

Firefighters so far have enacted voluntary evacuations of 15 to 20 homes and several pets in the area of the wildland fire burning near Willow, according to scanner traffic. The fire is burning closest to homes on Sharen Drive -- a dog mushing stronghold -- and Sockeye Avenue, and as of 4 p.m. another subdivision in the area of Little Willow Creek was also threatened, Matanuska-Susitna Borough spokesperson Patty Sullivan said. The borough is sending a trailer loaded with dog kennels to the Willow Community Center to help evacuate dogs, Sullivan said.

Firefighters are scrambling to protect several structures but much of the fire is burning and crowning in inaccessible areas, officials say. The fire has jumped the Parks Highway and is burning on both sides of the road, the state Division of Forestry posted on its Facebook page at 3:30. Alaska State Troopers are contacting residents in the area to alert them the fire is headed toward their homes.

Water-scooping aircraft from Fairbanks are en route, Sullivan said. Fire crews from White Mountain and Kenai are diverting to the Willow fire. The borough earlier issued an "all call" for all available tankers and any other resources in the Mat-Su. The Anchorage Fire Department is "on notice" to help if necessary, Sullivan said.

"It's pretty dire," she said.

Original Story: Homes were being evacuated Sunday afternoon as a human-caused wildfire burned north of Willow, the Alaska Division of Forestry reported.

The initial blaze was reported around 1:15 p.m. near West Sockeye Avenue, off Mile 77 of the Parks Highway, Division of Forestry spokesperson Tim Mowry said. In a Facebook post, the agency characterized the fire as "fast-moving." By about 2 p.m., the fire has spread to an estimated 30 acres, Mowry said.

"Some homes in the area have been evacuated but we do not know how many at this time," the division reported. Alaska State Troopers spokesperson Beth Ipsen reported about 10 homes and an unknown number of people had been evacuated. The Parks Highway was closed around Mile 77 at about 3 p.m., Ipsen said.

Firefighters and aircraft were responding to the fire.

"We do have at least one tanker (aircraft) that was based in Palmer that's done retardant drops on the fire," Mowry said, with multiple other aircraft on their way from Fairbanks to assist in the response. One helicopter was also dumping water at the scene, and another was on its way up from the Kenai Peninsula, Mowry said.

The exact cause of the fire wasn't yet clear, but officials were sure it was prompted by human activity.

"There wasn't lightning, which is the natural occurrence of fire," said Sam Harrel, spokesperson with the Alaska Fire Service. "Lack of that means it's human caused."