Six people have been killed in two states in a powerful March storm, officials said, as the severe weather system that brought blizzards to the Great Plains and high winds to the South continued to move across the US, NBC News reports.

The deaths—three in Nebraska and three in Mississippi—occurred Tuesday, authorities said.

More than 108 million people were under high wind advisories and 5 million more were under high wind warnings Wednesday afternoon as the storm continued to pose risks for an area from eastern Texas to Michigan and North Carolina, according to the National Weather Service. Many of those advisories later expired.

But on Tuesday, the storm caused severe winter weather in Nebraska that contributed to a head-on crash between a car and a tractor-trailer that killed three people, the Nebraska State Patrol said. Troopers responded to more than 300 weather-related traffic incidents, it said.

Damage assessments are underway.

A major low pressure system is causing the severe weather, the National Weather Service said. It was forecast to travel north and east across the Great Lakes and into southern Quebec through the day Thursday, it said.