SIOUX FALLS, S.D. -- As snowfall neared 4 feet in the Black Hills and winds gusting higher than 50 mph continued to howl, state officials had a simple message for anyone thinking of trying to drive in western South Dakota's blizzard: Don't.
And they stressed that the storm, which stranded an unknown numbers of motorists and knocked out power to thousands, would keep causing problems as it moves eastward Friday.
"This is a dangerous storm," Gov. Mike Rounds told reporters in a telephone conference call Thursday evening. "Western South Dakota is basically under a no-travel advisory."
Officials closed a long stretch of Interstate 90, where dozens of vehicles were trapped. Some motorists have been stranded for more than 24 hours, Rounds said, noting that search teams can't get to them because of zero visibility.
"We cannot see a thing in many areas where we're out actually searching for people," said Tom Dravland, state Public Safety secretary, adding that the top speed for some rescue crews was as little as a half-mile per hour.
Dravland said he did not know how many people were stranded. The Highway Patrol has responded to more than 400 calls for assistance, including 10 crashes. No fatalities were reported by late Thursday afternoon.
The storm already has dropped 45.7 inches of snow near Deadwood, in the northern Black Hills. Reports of 10 inches to 2 feet of snow were received from many West River counties. In some towns, residents reported drifts were blocking their doorways, and in the southwestern corner of the state, 20-foot snowdrifts were reported on the Pine Ridge Indian Reservation.
Dozens of schools, agencies, businesses and attractions, including Mount Rushmore National Memorial, were closed because of the snow, which started Wednesday afternoon.
Greg Harmon of the Sioux Falls National Weather Service office said winds should subside in the west early Friday and in the east later in the day. Blizzard warnings, winter storm warnings and winter weather advisories were issued for most of the Dakotas.
The wind and heavy snow caused many power failures, but repair crews can't get to the downed lines because of the blizzard, Rounds said. More than 10,000 customers lost power at some point in Nebraska and South Dakota.
According to the South Dakota Rural Electric Association, eight cooperatives reported outages and damage to their systems. Some people will be without power for several days, the governor said.
Eight inches of snow was reported in Richardton, N.D., southwest of Bismarck, and in Rushville, Neb., in the northwestern corner of the state, according to the weather service.
"The wind is blowing so hard it's hard to tell how much snow we got," said Terry Sarlsland, street superintendent in Bowman, N.D. "We got 4-foot drifts in some places."
Sharon Gjermundson, a postmaster in Taylor, N.D., said about a foot of snow kept her from punching in at work Thursday, and that she and her husband were worried about their livestock. "We hope all the cattle are OK," she said.Associated Press writers James MacPherson in Bismarck, N.D., and Josh Funk in Omaha, Neb., contributed to this report.