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Authorities searched for survivors Thursday after a powerful storm system that spawned multiple tornadoes tore through two North Texas neighborhoods, killing at least six adults.

As of daybreak, seven people were missing in the town of Granbury, which is just outside Fort Worth, authorities said at a press conference Thursday morning. It was not clear if they were were away from the area for other reasons.

At least one tornado was listed as an EF-4, which means winds can reach 200 mph.

"I've been assured by my deputies on the scene that they're pretty confident with the six that they found, but there was a report that two of these people that they found were not even near their homes. So we're going to have to search the area out there," Hood County Sheriff Roger Deeds said.

Deeds said he did not expect to find anyone else in the rubble. Search-and-rescue efforts were to wrap up by 10 a.m., The Dallas Morning News reported.

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MyFoxDFW.com reports as many as 10 tornadoes may have touched down as a result of the storms, one may have been a mile wide. About 50 people were taken to a Granbury hospital, where 14 were admitted for treatment of injuries and two were transferred to a hospital in Fort Worth, about 35 miles to the northeast, Deeds said.

Utility officials say about 20,000 homes and businesses have lost electricity.

Matt Zavadsky, spokesman for MedStar Mobile Healthcare, tells the Associated Press his company believes as many as 100 people were injured. Medstar sent three ambulances and a medical bus from its Fort Worth base to Granbury.

Hardest hit in Granbury were two neighborhoods, Rancho Brazos Estates and DeCordova Ranch, in the southern end of the town of about 8,000 residents about 65 miles southwest of Dallas.

Ambulances from as far away as Fort Worth were being called to Granbury, said Tye Bell, Richland Hills police spokesman who was heading to Granbury on Wednesday night.

Rancho Brazos Estates resident Elizabeth Tovar said she rode out the tornado with her husband and sister as she clutched her 9-month-old daughter.

"We heard the winds whipping and glass smashing everywhere," said Tovar, 25. "I felt like a long time and when things died down I looked up and saw that the roof was gone."

Another resident of that neighborhood, Allacia Jenny, said she witnessed devastation in her neighborhood.

"The house across from mine looked like it was destroyed," said Jenny, 22.

Toppled large trees litter her yard, and "I saw power lines all over the place," she said.

At Stumpy's Lakeside Grill in Lake Granbury, the storm took diners and workers by surprise. Some people rushed inside from the patio and ducked under tables as the wind gusts and hail started, but nobody was injured, said Eric Martinez, a cook. Then they looked across the lake and saw several homeowners' boat docks "just get torn apart," he said.

"The boat docks just flew off, and they're actually gone," Martinez said, adding that the boards and other debris landed in some yards.

The same storm spawned another tornado that storm spotters told the National Weather Service was a mile wide. That twister tore through the southwestern quadrant of Cleburne, a courthouse city of about 30,000 about 25 miles southeast of Granbury.

There were no reports of deaths in that storm, Cleburne Mayor Scott Cain said, "but we do have the potential for some injuries." He had no estimates.

Cain had no estimate on the number of homes damaged, but he said he expected the number to soar into the dozens based on his inspection of damage ranging from roof damage to total destruction.

Another tornado hit the small town of Millsap, about 40 miles west of Fort Worth. Parker County Judge Mark Kelley said roof damage was reported to several houses and a barn was destroyed, but no injuries were reported.

Hail as large as grapefruit also pelted the area around Mineral Wells on Wednesday evening. A police dispatcher reported only minor damage.

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The Associated Press contributed to this report