BUTLER, Pa.—Police were warning motorists to stay off the roads and closed others for several hours in the suburbs and counties north of Pittsburgh, where a brief spell of rain froze on roadways and led to crashes, including one that killed two children.

The National Weather Service says the icy spots developed because the ground remained cold enough from a recent cold spell despite temperatures in the low 40s.

State police in Butler, 30 miles north of the city, issued a late-morning plea Wednesday for people to stay off the roads temporarily, and police in Punxsutawney, 60 miles northeast of the city, reported multiple crashes.

Troopers from Butler say two children were killed when a woman's car slid on the ice, overturned, and crashed roof-first, into a tree in Butler County.