ANCHORAGE, Alaska — Two major highways south of Anchorage were closed Thursday while crews devised a plan to remove snow and debris and use military-style cannons to bring down other potentially dangerous avalanches.

The avalanche shut down both directions of the Seward Highway about 7 a.m. at its juncture with the Sterling Highway, the Alaska Department of Transportation said.

Seward Highway connects Anchorage to Seward on the Kenai Peninsula.

Sterling Highway, which goes to the scenic tourist town of Homer, also was closed.

It was uncertain how long the closure would last because work crews were assessing the situation, said Rick Feller, a spokesman for the Alaska Department of Transportation and Public Facilities.

Feller said the danger from avalanches in the area was considerable.

Seward Highway cuts through miles of mountains in Chugach State Park and Chugach National Forest.

"If you don't have to travel through the area, don't travel through the area," Feller said.

The closure was expected to extend well into the day.

The Seward Highway slide was estimated to be between 3 and 10 feet deep and 100 feet wide, considered a small to medium-sized avalanche.

The National Weather Service said the danger from avalanches had escalated Wednesday with a quick warm-up accompanied by a storm packing snow and hurricane-force winds.

Driving conditions along Turnagain Arm south of Anchorage also were particularly hazardous, with several school bus routes closed in Girdwood.

The Chugach National Forest Avalanche Information Center said the increased danger was caused by heavy snowfall, rain and strong winds that pounded the region. Avalanche danger is some areas of the backcountry is high, the center said, and it advised anyone without expert skills to keep away.

Moderate snowfall and strong ridge top winds were expected to continue Thursday in the Chugach.

Winds, which had abated in the Anchorage municipality, were expected to increase again Thursday and reach 80 to 90 mph south of the city.

The warm-up, and the accompanying avalanche danger, came on the heels of weeks of bitter cold in the middle of one of the snowiest winters on record for Anchorage.

As of Wednesday, snowfall for Anchorage totaled 90.5 inches — well above the season average of 74.5 inches, said Sam Albanese, National Weather Service's warning coordination meteorologist in Anchorage.

The city also is coming off the third coldest January on record, a month where the average temperature was just 2.9 degrees.

On Wednesday, an avalanche off Mount Roberts blocked traffic on Thane Road in Juneau. Police said the road would be cleared when it is safe, the Juneau Empire reported.

Poor weather in the Gulf of Alaska also prevented the ferry Kennicott from making its trip to Yakutat. The delay was expected to last at least 24 hours.