RAPID CITY, S.D. - A wintry blast of punishing wind and close to 4 feet of snow in places pummeled the Northern Plains on Thursday, stranding unknown numbers of motorists for a day or more and knocking out power to thousands. State officials said some people could be without power for days, but they had a simple message for anyone thinking of trying to drive in western South Dakota's blizzard: Don't. "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."

A long stretch of Interstate 90 was closed, and Rounds said most of the dozens of vehicles stranded along the stretch of highway had not been moved. Some have been stranded for more than 24 hours, he said, adding 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, who added 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 are 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 weather, which included wind gusts higher than 50 mph.

The snow started Wednesday afternoon and was moving east. Greg Harmon of the Sioux Falls National Weather Service (web|news) office said winds should subside in the west early Friday and in the east later in the day.

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.

In North Dakota, parts of Dunn County received about 9 inches of snow, the Weather Service said.

"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 that 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.