A strong winter storm has caused trouble for travelers, downed power lines to thousands of homes and caused deadly accidents in the midwestern United States.

In Dallas, Texas, icy conditions on Sunday prompted the cancellation of about 300 airline flights.

The storm also prompted the governors of Missouri and Oklahoma to declare a state of emergency.

Police in Oklahoma say icy roads were to blame for a head-on crash between a minivan and a tractor trailer truck that killed seven occupants of the van.

The seven were Mexican nationals. Five other occupants of the van were taken to the hospital.

Investigators said the minivan was hit after it skidded across the median of the divided highway Sunday morning about 180 kilometers west of Oklahoma City.

Some information for this report was provided by AP and Reuters.