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A mile-wide tornado touched down in north-central Texas as a storm system swept through with large hail and damaging winds, the National Weather Service said, promising more severe weather on Monday.

The storm knocked out power to more than 30,000 people in Texas, according to online reports compiled from local power companies. Austin Energy reported the most affected, with 7,600 without power.

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After moving through the town of Rio Vista, the tornado moved east into rural parts of Johnson County, Emergency Management Director Jamie Moore told NBC News. The tornado was about a mile wide when it was first spotted, he said.

The twister was spotted about 10:44 p.m. near Covington and near Cleburne State Park, about 25 miles south of Fort Worth, according to the weather service. "This is a particularly dangerous situation," it said.

Johnson County Emergency Management reported that semi-trailer trucks had been overturned, roofs were blown off, and roads were flooded, according to The Weather Channel. The agency also reported damage around the Rio Vista area, NBC Dallas-Fort Worth said. It said crew would be assessing the scale of the damage on Monday.

Tennis ball-size hail was reported near Glen Rose and Dinosaur Valley State Park, while softball-size hail damaged several vehicles near Stephenville, The Weather Channel reported.

Roads were impassable across much of southern Johnson County and damage, including missing roofs, was reported in Rio Vista, but the full extent was not yet clear. Johnson County Sheriff Deputy Casey Torrey said that deputies were out checking on damage reports. There were no immediate reports of injuries.

SOCIAL

Roads across much of southern JoCo are impassable. Please, do not get out and drive around. IT IS NOT SAFE YET. #dfwwx — Johnson County EM (@jocotx_em) April 27, 2015

11:01pm CDT radar scan showed another #tornado debris signature in Johnson County TX east of Rio Vista. pic.twitter.com/I9OXB7OoYX — Nick Wiltgen (@WxNick) April 27, 2015

BREAKING: A LARGE AND VIOLENT TORNADO REMAINS ON THE GROUND IN W OF GRANDVIEW (IF THERE) TAKE COVER NOW!!! — Storm Watch Dallas (@BreakingSWD) April 27, 2015

— M. Alex Johnson and Richie Duchon