A TORNADO emergency has been declared in Texas after storms hurled trailers through the sky and tore the roofs off family homes.
The National Weather Service (NWS) warned of two "large and extremely dangerous" tornadoes wreaking havoc across Dallas County and the Fort Worth area even as other twisters threatened to touch down in the coming hours.
There were no immediate reports of injuries but television footage showed tractor trailers being picked up by the storm and tossed hundreds of metres, bringing down power lines and lighting up the sky with electric sparks.
Large swathes of the area south of Dallas suffered major damage, including the suburb of Lancaster where the contents of houses was sucked into the street by the winds.
All flights from Dallas-Fort Worth International Airport were grounded and passengers moved into stairwells to shield them from breaking glass in the windows.
"Two tornadoes are currently affecting the DFW metroplex. Take cover now!" the NWS warned in an online statement.
Fears were growing for families in mobile homes which are likely to be torn from their moorings by the strong winds.
Cars and houses were pounded by chunks of hail larger than golf balls while there were unconfirmed reports of gas lines rupturing from the force of the storm.
Dallas County Sheriff Lupe Valdez told CNN that there had been no serious injuries so far, but officers had not investigated all of the damaged neighborhoods. Officers also had been dispatched to damaged areas to prevent looting, she said.
The US tornado season has started early this year. Tornadoes have been blamed for 57 deaths so far in 2012 in the Midwest and South, raising concerns that this year would be a repeat of 2011, the deadliest year in nearly a century for the unpredictable storms.
In 2011, there were 550 tornado deaths with 316 lives lost on April 27 in five southern states, and a massive tornado that killed 161 people in Joplin, Missouri on May 22.