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"The images from across Mississippi are heartbreaking," Mr Biden said in a statement. "We will do everything we can to help. We will be there as long as it takes."
Mississippi Governor Tate Reeves said he spoke with Mr Biden about the deadly tornadoes they faced overnight. "... He assured us FEMA would be there to support our response. The flood of support from governors, businesses, charities, and federal admin has been tremendous - matches the community here on the ground," Mr Reeves tweeted, referring to the Federal Emergency Management Agency (FEMA).
The powerful storm system that generated the tornado, accompanied by thunderstorms and driving rain, cut a long path across Mississippi late Friday, slamming several towns along the way.
Malary White, a spokesperson for the Mississippi Emergency Management Agency, said damage assessments would not be possible until officials could do a complete survey in the daylight.
"Our main priority right now, especially for the local first responders, it's life safety and accounting for the people and making sure they are safe," Ms White told CBS News affiliate WJTV.
In the hard-hit town of Rolling Fork, all that was left of an entire row of houses and buildings was scattered debris. Cars were overturned and smashed, fences were ripped up and trees uprooted, according to local television footage.
"My city is gone," Rolling Fork Mayor Eldridge Walker told CNN. "Devastation - as I look from left to right, that's all I see."
Resident Shanta Howard told ABC affiliate WAPT that locals had to help remove the dead from the wreckage of their homes. "It was like no notice. We didn't know what was happening," a tearful Tracy Harden, the owner of Chuck's Dairy Bar in Rolling Fork, told CNN.
The National Weather Service warned residents that as clean-up operations continue, "dangers remain even after the storms move on." A local tornado watch expired in the early hours of Saturday, meteorologists said. More thunderstorms were expected, but they were not forecast to be severe.
Tornadoes, a weather phenomenon notoriously difficult to predict, are relatively common in the US, especially in the central and southern parts of the country.
With inputs from AFP
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