Residents of Midwestern states mourned their dead Sunday after a string of killer tornadoes tore through the US heartland, killing at least 38 people, injuring hundreds and virtually wiping out entire communities.

Church services were to be held throughout the stricken region as stunned Americans grappled with the magnitude of the destruction brought by Friday's twisters.

More trials, however, were in store for the disaster area. While tornado watches were discontinued, the National Weather Service forecast a cold front with possible snow.

Temperatures were expected to fall below freezing by Sunday night and a mix of rain and snow was to become all snow, the service warned, a development that could pose a challenge for people left without homes.

President Barack Obama called the governors of Indiana, Kentucky and Ohio to offer condolences for the dead and said the federal emergency management agency stood ready to help, the White House said.

Deaths were reported in Indiana, Kentucky, Ohio, Alabama and Georgia as the storm system moved eastward.

"The scope and magnitude of devastation in some of our communities is unlike anything I have ever seen," said Kentucky governor Steve Beshear, whose office confirmed 19 fatalities from over a dozen tornadoes that had roared across the state.

Trucks and trees were upended as deadly funnel clouds ravaged parts of eight states in the US Midwest and South.

The devastating images included a school bus smashed through the wall of a house, trucks thrown into lakes, solid brick homes reduced to rubble and wooden ones smashed into kindling, as well as mobile homes flipped like tin cans.

About 300 injuries have been reported in Kentucky, according to Beshear, who surveyed the damage in the devastated town of West Liberty. There was damage in 40 counties with power supplies to tens of thousands knocked out.

Amateur video aired on CNN showed a gargantuan grey twister churning over West Liberty on Friday, as a woman loudly prayed "Oh God, take it away from us Lord!"

At least 14 people were killed in Indiana, according to Governor Mitch Daniels, who inspected the devastation in Henryville.

"We're not unfamiliar with Mother Nature's wrath out here in Indiana, but this is about as serious as I've seen it in my years in this job," an emotional Daniels told reporters.

"Lucky it wasn't worse," he said, adding that while early warning systems likely saved lives, it was a "heartbreaking" loss for families.

The high school in Henryville suffered damage, but luckily all the children were evacuated safely and only minor injuries -- some cuts and scrapes -- were reported, said sheriff department spokesman Chuck Adams.

Officials in Clark County, Indiana were scrambling to deal with widespread damage after roads were blocked by fallen trees and debris, and power and phone lines were knocked out.

The hardest hit was Marysville, where the small town has nearly ceased to exist, officials said. "That's the information we have, that Marysville is no longer," US Senator Dan Coats of Indiana told CNN.

The only good news amid all this death and devastation was a report that a two-year-old girl survived a terrifying tornado that killed her parents and siblings.

The unidentified toddler was found lying among the bodies of her family in a field near a flattened home in New Pekin, Indiana, said hospital staff.

"She continues to remain in critical condition," Cis Gruebbel, a nurse at Kosair Children's Hospital in Louisville, in neighboring Kentucky, told local media.

Indiana activated 250 members of its National Guard, who used Black Hawk helicopters to reach hard-hit regions. Indiana and Kentucky declared states of emergency.

There were three deaths in neighboring Ohio, including a city councilwoman from the town of Moscow, an Emergency Management Agency official said.

The Gulf Coast state of Alabama reported one death after tornadoes trapped people in rubble, destroyed houses and uprooted trees.

For Brandy Robbins, whose home in Harvest, Alabama was destroyed in devastating tornadoes last year, it was a sickening case of deja vu.

"I realized lightning does strike twice," she told Fox News, standing outside the home she recently rebuilt, only to have it badly damaged once more.

"Unfortunately my kids and I are going to have to rebuild again."

In Georgia, a woman was killed in the city of Alpharetta, north of Atlanta, and tornadoes inflicted severe damage on at least 40 homes and a regional airport west of the city in Paulding County, a spokeswoman for the state's emergency management agency said.

The latest wave of storms comes as people were picking through rubble left behind by a string of twisters across six states that killed 13 people earlier in the week.

The NWS received 83 reports of tornadoes in eight states by Friday evening, bringing the week's total to 133.

Some 545 people were killed by tornadoes in 2011, the deadliest season since 1936 and the third worst on record.

This year tornadoes have come early with the mild winter creating the conditions for cold fronts to slam into warmer air.

"We knew it was going to be bad," said Angie Lese, a meteorologist with NWS. "All the ingredients came together for a significant outbreak."