More than 4 million people across five states were under winter storm alerts on Sunday as heavy lake-effect snow continued to bury the Great Lakes region, prompting emergency declarations and the deployment of National Guard troops to rescue stranded motorists.

The lake-effect snowstorm has disrupted holiday travel across the region. Some areas could get up to six feet of snow by Tuesday.

The snowfall was heaviest along Interstate 90, the National Weather Service said, which hugs Lake Erie from Buffalo, New York, and on to Cleveland.