Photo: The Canadian Press

Tornadoes touched down in the upper Midwest and northern Arkansas on Tuesday as a spring-like storm system posed a risk to 45 million people. Hail fell so quick that motorists had to pull over and stop in Missouri.

Minor injuries were reported at a nursing home southwest of Chicago, while structural damage was also reported at Higginson, Arkansas, about 50 miles northeast of Little Rock.

Forecasters were particularly concerned that the worst of the weather developed after nightfall — and worried it would continue overnight and hit communities while people slept.

The Storm Prediction Center said 45 million people from Texas to Ohio faced some risk of bad weather, and that the area from the southwest Missouri into Indiana faced a "moderate risk" for significant storms. The unstable atmosphere was expected to produce significant storms later Tuesday.

A twister hit the LaSalle County Nursing Home in Ottawa in central Illinois. A woman answering the telephone at the nursing home said several residents reported bumps and bruises but no serious injuries. Trees and power lines were also down in the area.

Hundreds, including many school children, took shelter at Bald Knob High School after a tornado warning was posted for the area. The school is hosting a state basketball tournament for smaller schools this week. Moments earlier, the storm caused damage in Higginson, a town of 621, the White County Sheriff's Office said.

"The tournament is on hold until the weather passes," dispatcher Jordan Smith said.

The Bald Knob storm was part of the same system that produced a wall cloud near Mayflower, Arkansas, which was hit in 2014 by a tornado with winds approaching 200 mph. The storm crossed Interstate 40 between Little Rock and Conway, but there were no reports that a funnel cloud touched down.

The Storm Prediction Center had warned that some of Tuesday's storms would track over long distances. The Arkansas storm held together for more than 100 miles, though it did not produce tornadoes over its entire path.

Drivers stopped along U.S. 60 east of Springfield, Missouri, according to the Wright County Sheriff's Office. Reports filed with the National Weather Service said the thunderstorm dropped hail the size of half dollars.

The greatest risk for strong twisters was in an area from Poplar Bluff, Missouri, to Louisville, Kentucky, though the area from Arkansas to Ohio would also be affected. Forecaster Ariel Cohen, who raised Tuesday's threat level in a midday update, said sunshine warmed the region and roiled the atmosphere ahead of an approaching cold front.

The threat is expected to shift into the southeastern states Wednesday.