Story highlights Resident says she's been told power will be out three weeks

National Weather Service says at least 13 tornadoes touched down

Doctor says some victims had to have amputations

Roof collapsed, "and you could see the twister just there, basically," witness says

Chainsaws wailed Thursday in Granbury, Texas, as some residents began to clear fallen trees and whittle down the mounds of household goods strewn across the landscape, a testament to the ferocity of the previous night's tornadoes.

But other residents, those from the hardest-hit neighborhoods, had to wait, hoping to hear when they could go back to their damaged and leveled homes to see what remains.

Ronna Cotten said she has been told she can't re-enter her subdivision to "check to see if we have any belongings left" for at least two days, maybe as many as seven.

Power is expected to be down for the next three weeks, Cotten said she was told. Cotten stayed in the home of a woman who picked her up from the rescue center Wednesday night and worked the phones Thursday trying to find hotel rooms for her family.

She still considers herself fortunate.

"I feel very lucky because we are alive" said the mother of four, who clutched a doorknob to keep the closet door shut as winds tore through her home.

Rescue crews searched for seven people missing after the tornadoes struck this town in North Texas, killing at least six.

A witness described getting an uncomfortably close view of the storm.

"One second you could see the whole roof collapse, and you could see the twister just there, basically," the man told CNN affiliate KTVT . "It was horrible."

He and his family of five had crowded into the bathroom for shelter when the storm hit, he said.

"We were just watching the hail go by and then it just happened in the blink of an eye," a woman said.

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Photos: Photos: Tornadoes hit North Texas Photos: Photos: Tornadoes hit North Texas Tornadoes hit North Texas – Texas Gov. Rick Perry, center, and Texas Attorney General Greg Abbott, left, survey the tornado damage in the Rancho Brazos Estates subdivision near Granbury, Texas, on Friday, May 17. At least six people were killed in a string of tornadoes that struck overnight Wednesday in North Texas. Hide Caption 1 of 15 Photos: Photos: Tornadoes hit North Texas Tornadoes hit North Texas – A heavily damaged home can be seen in this aerial view on Thursday, May 16, in Cleburne, Texas. Hide Caption 2 of 15 Photos: Photos: Tornadoes hit North Texas Tornadoes hit North Texas – Beth Poledna walks through her garage on May 16 in Cleburne, Texas, as she begins the cleanup after a tornado swept through the area. Hide Caption 3 of 15 Photos: Photos: Tornadoes hit North Texas Tornadoes hit North Texas – An upturned vehicle lies next to an uprooted tree on Thursday, May 16, in Granbury, Texas. Hide Caption 4 of 15 Photos: Photos: Tornadoes hit North Texas Tornadoes hit North Texas – Debris from damaged homes litters a neighborhood in Granbury on Thursday, May 16. Hide Caption 5 of 15 Photos: Photos: Tornadoes hit North Texas Tornadoes hit North Texas – Rescue workers search through debris in Granbury, on May 16. Hide Caption 6 of 15 Photos: Photos: Tornadoes hit North Texas Tornadoes hit North Texas – A rescue worker sifts through rubble on May 16 in Granbury, southwest of Fort Worth. Hide Caption 7 of 15 Photos: Photos: Tornadoes hit North Texas Tornadoes hit North Texas – Rescue personnel pass remnants of destroyed houses in Granbury on May 16. There were reports of homes in Granbury being flattened with people inside. Hide Caption 8 of 15 Photos: Photos: Tornadoes hit North Texas Tornadoes hit North Texas – Pete Alaniz eyes damage to the garage of his Cleburne, Texas, rental home on May 16. Hide Caption 9 of 15 Photos: Photos: Tornadoes hit North Texas Tornadoes hit North Texas – At least 10 tornadoes touched down in northern Texas late Wednesday May 15, including this one in Millsap, west of Fort Worth. Hide Caption 10 of 15 Photos: Photos: Tornadoes hit North Texas Tornadoes hit North Texas – The living room of a Cleburne home is left without a roof on May 16. Hide Caption 11 of 15 Photos: Photos: Tornadoes hit North Texas Tornadoes hit North Texas – An antique car sits in a collapsed garage on May 16 in Granbury. Hide Caption 12 of 15 Photos: Photos: Tornadoes hit North Texas Tornadoes hit North Texas – Eva Zapata, left, waits with a relative, Dario Segura, on May 15 for news of her children, who live in the Granbury neighborhood of Rancho Brazos. Six of the storm victims came from that subdivision, the Hood County sheriff said. Hide Caption 13 of 15 Photos: Photos: Tornadoes hit North Texas Tornadoes hit North Texas – John Bouyer collects a refrigerator on May 16 that blew away from his sister-in-law's home in Granbury. Hide Caption 14 of 15 Photos: Photos: Tornadoes hit North Texas Tornadoes hit North Texas – A trailer rests against a garage in Cleburne on May 16 after being blown into a house. Hide Caption 15 of 15

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Nearby, a water heater was on its side; an upside-down car, its windows shattered and its silver skin crumpled, lay helpless in the dirt. A wheelchair lay in pieces a few feet away.

Video shot from a helicopter showed rafters still intact, but the roofs they supported were gone.

Hood County Sheriff Roger Deeds identified those killed as Jose Tovar Alvarez, 34; Marjari Davis, thought to be 82; Tommy Martin, 61; Leo Stefanski, 83; and Robert and Glenda Whitehead.

Deeds said search and rescue operations to find survivors "are pretty much winding down."

"We're going to keep on looking," Deeds added. "We're not going to give up until every piece of debris is turned over."

Rescuers had walked through the hardest-hit subdivision in Granbury "over and over and over again," Deeds said earlier in the day. "I'm confident we haven't left anybody behind, but we're still checking."

Granbury is 30 miles southwest of Fort Worth.

The deaths occurred in a neighborhood of about 110 homes, many of which were built by Habitat for Humanity. Most of the homes in the Rancho Brazos subdivision were destroyed or damaged, the sheriff said. That is where the missing live, too, he said.

Mayor Pro Tem Nin Hulett told CNN's Anderson Cooper that there were indications those people may be on vacation or in other areas, but officials were working to confirm that.

People whose lives had been hit by the twisters were asking to get back to their homes, but the sheriff said he wasn't convinced it was safe for civilians to be in the area yet.

Three people were taken to an area hospital, and 13 others were taken to hospitals in the Dallas-Fort Worth metroplex, he said.

Some of the patients had to have amputations, Dr. Kerri Sistrunk, head of the trauma unit at Lake Granbury Medical Center. Others suffered head injuries and open fractures, as well as minor abrasions, she said.

At least 13 tornadoes touched down in the area, the National Weather Service said. A survey team said it found damage indicating an EF4 tornado had struck. That is the second-most severe classification on a scale of zero to five,

Several of the tornadoes struck Cleburne, about 30 miles east of Granbury.

"I was actually standing outside on my front porch and watched (a) tornado come across," Robert Barnett told CNN affiliate WFAA . "I've seen tornadoes before -- I've chased them -- but I've never seen one like this. It freaked me out."

Another resident said he thought the storm had passed but was wrong.

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"I went back outside and saw stuff flying by and said 'It's here! Let's go!'" Darrin Vasquez told the station. He lost part of the roof on his home and when rain flooded in, a ceiling collapsed.

WFAA said at least 12 homes lost their entire roofs.

In nearby Ellis County, a suspected tornado knocked out power in the city of Ennis about midnight, said Steve Howerton, city manager.

"Several buildings in the downtown historic district have been seriously damaged," he said.

"There are a lot of traumatic injuries," said Donna Martin, a worker at a local veterans' organization. "My husband told me that a car was lifted in the air. It just came in and hit so fast."

B.B. French, who lives on a canal three miles from where the worst of the damage occurred, said she was lucky.

"We had extreme winds," the 71-year-old resident said in a telephone interview. "And then the sirens went off and then I got inside."

As lightning flashed and rain poured, she watched from inside her home as two mallards lay on the pavement. "They just laid down on the sidewalk until the hail came, and then they were smart enough to waddle over and get underneath the roof" of her boat deck.

After the storm passed, French went outside to find that her neighbor on one side had lost a few shingles from his roof; on the other side, a neighbor had lost a couple of shutters; but her house was unscathed.

"It really is just luck," she said.