Powerful spring storms roared through parts of the U.S. South on Friday, toppling trees, smashing buildings and killing at least nine people, including two sets of parents and children who were huddled together as the winds raged outside their homes.

It was the deadliest storm of the season so far. Several tornados accompanied the onslaught, but much of the damage was attributed to straight-line winds — sudden, violent downbursts that struck with hurricane force in the middle of the night.

Forecasters warned of approaching danger as much as three days earlier, but the winds up to 130 km/h and repeated lightning strikes cut a path of destruction across a region so accustomed to violent weather that many people ignored the risk — or slept through it.

The storms began late Thursday in Oklahoma, where at least five tornadoes touched down and two people were killed. The system then pushed into Arkansas, killing seven more. Dozens of others were hurt.

By midday Friday, the storms marched into Tennessee, Louisiana and Mississippi. At least three tornados touched down in Mississippi, causing widespread damage but only one serious injury.

Powerful straight-line winds

Arkansas Gov. Mike Beebe said he had never seen the state suffer so many deaths from straight-line winds. Tornadoes and floods cause most of Arkansas storm-related fatalities.

A six-year-old boy was killed in this house on Friday near Bald Knob, Ark., when a tree was blown over. (Warren Watkins/Daily Citizen/Associated Press)

"Just trees blowing on people's residences — I don't recall anything even approaching this," Beebe said.

Unlike tornadoes, which develop from columns of rotating air, straight-line winds erupt from a thunderstorm in unpredictable downdrafts, then spread across the landscape in all directions.

Teams from the National Weather Service worked Friday to learn more about what caused the damage.

At Crystal Springs, Ark., lightning split a tree that fell into a home, killing an 18-month-old girl and her father as they slept. In Little Rock, winds knocked a tree into a home, killing a woman and her eight-year-old son in his bed.

In the Arkansas town of Bald Knob, six-year-old Devon Adams died when the top of a tree more than in diameter crashed through his home while he was sleeping.

Twister devastates Oklahoma town

Residents of the small town of Tushka, Okla., wondered what would become of their community after a twister damaged or destroyed nearly every home along the two main streets. The only school — a collection of buildings housing kindergarten through Grade 12 — was all but gone.

"It's hard to deal with because we're a small community with limited resources. It's hard to do the cleanup," Mayor Brickie Griffin said.

At least 25 people were hurt as the tornado plowed through the town of 350 before dawn. At least a dozen homes and businesses were destroyed.

The school was to stay closed for the rest of the academic year, and officials were looking for an alternate place to hold classes.

Gilbert Wilson, Atoka County's emergency management director, said witnesses reported seeing two tornadoes that merged into a single twister. The weather service confirmed a tornado hit the area.

The owner of the Atoka Trailer Manufacturing plant said it would cost millions of dollars to rebuild the factory, which made trailers for hauling heavy equipment.

"Twenty-four hours ago, this was an 80,000-square-foot heavy manufacturing facility. At the moment, it's a pile of rubble," Ryan Eaves said. "This building was a shining bright spot for the community. To think it could be overtaken like this is overwhelming."

He said he would shift work for the plant's 60 employees to another factory five kilometres away.

Authorities said a strong downburst of wind apparently overturned a mobile home, killing a 64-year-old woman in St. Francis County, in eastern Arkansas.

In Little Rock, the storms intensified shortly before 2 a.m., catching many people asleep. But the city's sirens were wailing when the weather hit.

One man was killed when a tree fell on his recreational vehicle.

A woman identified as a nurse and her eight-year-old son died when an oak tree fell into the boy's bedroom. A baby sleeping in a nearby room was not injured, police said.

At daybreak, the tree still leaned against the home's back bedroom, exposing some of the little boy's treasures: a stuffed frog, a toy truck.

A few of the woman's fellow nurses huddled around her sister outside the home.

"She doesn't even want to come near the house," said Theresa Travis, a doctor who worked with the dead woman, who had not been publicly identified.