Emergency workers spent early Monday going door to door in search of other victims.
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"Once we get daylight, we will be able to identify areas that are affected and lead responders in to verify the [houses] are clear of any individuals needing medical attention," Allen said.
The American Red Cross was also on the scene and establishing a shelter in a local church.
The severe weather struck around 8:45 p.m. local time (9:45 p.m. ET). It was one of at least 26 tornadoes reported across the U.S. on Sunday.
The area also saw heavy rains and widespread flash flooding. Two groups of people had to be airlifted to safety on Sunday, authorities in Denton County said.
More than 5 inches of rain fell in Navarro City in just a few hours, prompting a flash flood emergency, NBC Dallas-Fort Worth reported.
Meanwhile, up to 50 million Americans were in the line for a wet and windy Monday as a band of thunderstorms and severe weather stretched down the country's midsection.
According to The Weather Channel's Kevin Roth tornadoes remained a hazard on Monday with coastal Texas, including Houston, staying under a tornado warning until noon local time (1 p.m. ET), he said.
"Anywhere from eastern Texas up to southern Michigan there is a threat of tornadoes in the mid-to-late afternoon," Roth added.
A rare May snowstorm that brought more than a foot of snow to parts of South Dakota and Wyoming was set to end by Monday morning, according to forecasters.
The remnants of Tropical Storm Ana was also set to continue drenching North Carolina. Meteorologists warned that minor flooding was possible.
—The Associated Press contributed to this report.