Hundreds of thousands of customers are without power across the Midwest after deadly, severe weather battered the region — and the threat is continuing along the East Coast.

The severe weather first struck the Midwest on Sunday, leaving nearly 300,000 customers without power in Michigan on Monday. Another 50,000 are without power in Wisconsin and 40,000 are in the dark in Indiana.

There were more than 400 reports of severe weather related to powerful wind gusts, wind damage and large hail, and at least six tornadoes were reported across multiple states.

Five fatalities have been attributed to the storm.

Three children — a 2-year-old girl, her 4-year-old brother and their 11-year-old cousin — were killed when the minivan they were in was hit by a large tree in Michigan, the Kalamazoo County Sheriff’s Office said.

Weather appeared to be the main contributing factor, the sheriff’s office said.

The “high winds … came down fast,” Sheriff Richard Fuller told reporters.

“There’s no vehicle that would stand up to this,” he said, adding that there was “nothing anybody could’ve done.”

In Valparaiso, Indiana, one person was killed when “severe crosswinds” blew a tractor and a trailer onto their sides, according to local authorities.

The National Weather Service said a second person was killed north of Millersburg, Indiana, when wind from a thunderstorm blew over an Amish buggy.

The severe weather threat continues on Monday with a focus on the East Coast.

A dangerous line of storms pounded the Atlanta area with wind on Monday morning, and now the threat is moving north.

Severe thunderstorm watches are in effect in Florida, Georgia, South Carolina and North Carolina. Isolated tornadoes, damaging wind gusts and large hail are possible.

Around the evening rush hour, isolated thunderstorms will begin to pop up in the Northeast, including New York City.

The heavy rain and thunderstorms will become more widespread into the night.

Damaging wind gusts and lightning are expected.

This deadly system will be gone by Tuesday morning.

ABC News’ Darren Reynolds and Jessica Gorman contributed to this report.