A severe winter storm has killed at least three and left almost half a million energy customers without power on Monday morning, as strong winds and heavy rain caused havoc from the Mid-Atlantic to the South.

“Large hail, damaging winds, and a few tornadoes can all be expected” over the Ohio, Tennessee and Mississippi Valleys, through the Mid-Atlantic, Southeast and Gulf Coast, the National Weather Service said in an early Monday forecast.

More than 70 million were under various weather alerts Sunday night.

The Porter County Sheriff’s Office confirmed that a man died on Sunday in Valparaiso, Indiana, when his semi-truck and trailer were blown over in winds of up to 80 mph. The victim was identified as 34-year-old Jagbir Singh, and there were widespread reports of trees being knocked down or uprooted in strong gusts.

A man was killed in Cherokee County, Oklahoma, when a tree fell into a camper just before 2 a.m. on Sunday, NBC affiliate KJRH of Tulsa reported, citing local officials.

A preliminary report from the NWS office in northern Indiana said that one person was killed when an Amish buggy was toppled over in high winds in Millersburg, Indiana. NBC News contacted law enforcement officials but did not receive confirmation of this report until early Monday.

The city of Elkhart, Indiana, said that while there were no fatalities overnight, there was extensive damage, including a collapsed building. Police warned people not to leave their homes unless it was “absolutely necessary.”

The NWS urged people under a tornado watch to know where their nearest shelter is and to immediately go there. One resident in Vancleave, Mississippi, posted footage online on Sunday showing an enormous funnel cloud. Another potential tornado was filmed in Doniphan, Missouri, against a backdrop of dark, foreboding clouds.

Freezing rain and high winds brought down power lines across the Great Lakes region, from Michigan to Wisconsin, while forecasters warned that the severe weather is headed south and could reach Tennessee.