At least three people have died as a powerful winter storm moves east across the US, spawning tornadoes in southern states and coating others in snow.
A young boy and his mother were killed in Louisiana when their home was destroyed by a tornado.
The huge storm also brought blizzard-like conditions to the Midwest, with roads and schools closed and some areas reporting 4ft (1.2m) of snow.
Around 3,300 flights have been delayed and over 150 more cancelled.
Some 500,000 people across four states - Nebraska, Wyoming, South Dakota and Minnesota - are under blizzard warnings, with powerful winds and heavy snowfall making travel difficult. Millions more around the country are under less severe winter weather alerts.
Severe storms are forecast along the Gulf coast, including in Louisiana, Mississippi, Alabama and parts of Florida. There are also tornado warnings in parts of Louisiana and Mississippi.
Rescuers searched for hours before recovering the mother and son who died in a rural area near the city of Shreveport.
The remains of the boy - Nikolus Little, eight - were found in a wooded area half a mile from the family home.
The body of his mother - Yoshiko A Smith, 30 - was discovered about one street away from the destroyed home, under a pile of debris, officials said.
Sheriff Steve Prator told the local television station KSLA that the father had reported them missing.
"We couldn't even find the house that he was describing with the address," said the sheriff. "Everything was gone,"
A 56-year old woman was also found dead outside her home in St Charles Parish, according to a local politician. The Louisiana Department of Health said she died after a tornado destroyed her house.
In the small town of Farmerville about 100 miles (160km) away, at least 25 people were hurt after a tornado hit, according to local news outlet KNOE.
At least 18 tornadoes touched down in Texas, Louisiana, Oklahoma and Mississippi on Tuesday, injuring residents and wrecking homes and buildings.
More were reported on Wednesday, while Louisiana's governor declared a state of emergency.
Most of the US is likely to feel some impact from the storm, with cold weather and snow forecast as it moves east over the coming days.
"It's a fairly vigorous storm system," Rich Otto, a meteorologist with the Weather Prediction Center, told the BBC. "This one is a little larger than your average winter storm."
The severe weather has caused hundreds of flight disruptions at Dallas Fort Worth International Airport in Texas and Denver International Airport in Colorado over the past two days, according to FlightAware.com.
The storm has also spilled into Canada, bringing heavy snow and high winds in the country's southern Prairie region, including the provinces of Saskatchewan and Manitoba.
Freezing rain and other wintry conditions are forecast to hit the upper Midwest and north-eastern US on Thursday, the National Weather Service said.
The storm system began to hit the US last Friday, bringing powerful winds and snow to parts of California.
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