ANCHORAGE — Two wildfires burning north and south of Anchorage stretched Alaska firefighting resources Tuesday as crews scrambled to protect rural homes and cabins.

The human-caused Sockeye Fire grew but consumed no new structures around the community of Willow, about 40 miles north of Anchorage. It started Sunday and has blackened 12 square miles along the Parks Highway, the main route between Anchorage and Fairbanks.

Through Monday, the fire had burned 25 homes and 10 to 20 other structures. About 1,700 structures are in a voluntary evacuation zone.

The Card Street Fire grew from 1 square mile to 2.3 square miles near the community of Sterling on the Kenai Peninsula, about 60 miles southwest of Anchorage. It started Monday and destroyed six structures.

On Tuesday, temperatures extending into the mid-80s, low humidity and the possibility of dry thunderstorms throughout southcentral Alaska kept authorities on high alert.

“It’s going to be another red-flag warning day,” said Tim Mowry of the Alaska Division of Forestry and a spokesman for the Alaska Interagency Coordination Center.

Willow is an unincorporated community of 2,000 spread along 20 miles of the Parks Highway. Roads lace the forest and lead to smatterings of cabins and year-round homes.

The Susitna River is a natural barrier west of the highway. Firefighters are using Alaska Railroad tracks as a firebreak on the east side of the highway.

The Sockeye Fire spread Monday in the northeast and southeast corners on the west side of the highway and remains uncontained, Mowry said. The blaze tends to spread most during the day and slows at night, he said.

“We’ve got crews that are working round the clock,” he said, and battling the fire at night allowed them to make gains.

Firefighters used the forest roads to protect structures and keep the fire out of the neighboring highway communities of Caswell Creek and Montana Creek to the north. The more populated towns of Houston and Big Lake are to the south.

“We don’t want the fire getting anywhere near those communities,” Mowry said.

Nearly 300 people are working on the fire.

Some of the structures in the voluntary evacuation zone are better protected than others, Mowry noted.

“We get a lot of calls from people who want to get into their houses now and cut trees down around their house and do stuff that they should have been doing a while ago,” he said.

The fire on the Kenai Peninsula near Sterling was reported Monday as a 1-acre grass fire off Card Street, which branches south off the Sterling Highway.

Three tankers took to the air to drop retardant. Fire trucks from Central Emergency Services patrolled Funny River Road on the south side of the Kenai River to extinguish spot fires started by embers floating across the water.

“They were chasing these spots with a helicopter and a boat,” Mowry said.

Firefighters caught a break when winds shifted Monday night, pushing the fire east into wetlands.

About 50 people are working on the fire, and five ground crews were scheduled to arrive Tuesday.

By Tuesday afternoon, the fire had pushed east away from homes and private land into the Kenai National Wildlife Refuge, said Alaska Division of Forestry spokesman Andy Alexandrou. The east edge was about 1.5 miles south of the Sterling Highway at the west end of Skilak Lake Road.

The situation is the opposite of last year. The Funny River Fire in 2014 burned more than 300 square miles, mostly south of the Kenai River in the Kenai National Wildlife Refuge. It threatened to jump the river to neighborhoods where the Card Street fire is now burning.