One man describes "white-out" conditions in Indianapolis
Twelve people have been reported killed by a severe snow storm now moving into north-eastern US states after disrupting Christmas in the Midwest.
States in New England are due to see heavy snowfall, with up to 18 inches of snow expected in parts of Maine, the National Weather Service said.
Flights were grounded and road collisions reported as the storm moved across the middle of the US.
Meanwhile, as many as 34 tornadoes were reported across the South on Tuesday.
The storm moved across the Upper Ohio Valley and into the US north-east on Wednesday night. Heavy snow was also reported in eastern parts of Canada.
Winter storm warnings issued by the National Weather Service on Thursday said temperatures could dip to nearly 20F (-6C) and warned of dangerous travel conditions with near-zero visibility on roads.
Storm-related deaths were reported in Ohio, Indiana, Arkansas, Oklahoma, Texas, Louisiana, Pennsylvania and Virginia, the Associated Press (AP) said.
'Sleet and freezing rain'
US storm update
As much as 12in to 18in (30.5cm to 46cm) of snow could fall in parts of Maine on Thursday, the latest weather advisory added.
In Concord, New Hampshire, resident Dale Lamprey said he had been on the streets before 05:00 EST (10:00 GMT) on Thursday morning, trying to clear the snow.
"It's been windy, it's been snowing and I think it changed over to sleet and freezing rain at one point. It's pretty bad," he told the Associated Press news agency.
Inbound flights were delayed in Philadelphia and at New York's LaGuardia airport, as thousands of travellers were trying to return home after Christmas.
Flights were also cancelled in Canada, with Toronto and Montreal affected, reports said.
Earlier in the week Little Rock, Arkansas, saw its first snow on Christmas Day in 83 years, while in neighbouring Oklahoma seven inches of snow were blamed for a 21-vehicle pile-up on an interstate highway outside Oklahoma City.
Thirty-four tornadoes were reported in the southern states of Texas, Louisiana, Mississippi and Alabama on Tuesday. A large section of a church roof in Mobile, Alabama, was ripped off by a twister.
Falling trees claimed the lives of two people in Texas and Louisiana. Deaths were also reported on the roads in Oklahoma and Arkansas.
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