Officials in Johnson County, about 54 miles south of Dallas, said they had evacuated about 12 people caught in flooding overnight — including some rescued from "homes inundated with water."
Other incidents involved vehicles and authorities instructed residents to stay off the roads for their own safety.
Johnson County emergency management coordinator Jamie Moore told NBC News that 45 roads had been closed in the area by 3:30 a.m. (4:30 a.m. ET). About an hour earlier, his agency tweeted that "rescue requests continue to flow in."
In Austin, emergency workers recovered a houseboat with about 20 people aboard that went adrift in the record floodwaters.
Flood warnings were issued for 21 communities and flash flood warnings for six, including western Dallas, according to NBC Dallas Fort-Worth. Hail, tornadoes and thunderstorms also remained a possibility.
About 56,100 people were without power throughout the Texas as of 3:30 a.m. ET.
Officials have been closely watching rising rivers and creeks in Texas after heavy rains last weekend. At least 23 people have died in flooding across the state this week.
The hardest-hit area on Thursday night was the corridor running from Laredo on the border with Mexico up through Dallas and over into Oklahoma into Oklahoma City, according to The Weather Channel's Michael Palmer.
Palmer added that the past month had been the wettest May since records began in the late 1800s.
More than 100 flights were canceled going in and out of Dallas-Fort Worth International Airport on Thursday and Friday, according to FlightAware.com.
Dallas officials warned commuters to be extremely cautious while driving.
"If you see water on the roadway even if you think it is one inch don't attempt to drive through it ... if there are barricades up on the road, they're there for a reason," Dallas' assistant emergency management coordinator Kevin Oden told NBC News.