(CNN) -- St. Louis awoke to tornado sirens Thursday as a cluster of heavy thunderstorms swept through the central United States, bringing the threat of heavy rain, high winds and possible twisters to millions in its path.
Tornado and flood watches were posted from the southern Great Plains to the Ohio River Valley, but the greatest risk of damaging storms fell from the Ozarks through western Tennessee, the National Weather Service reported.
The weather service confirmed a tornado touched down about an hour before sunrise in University City, Missouri, gouging a half-mile-by-100-yard path through that St. Louis suburb. The weather service gave the tornado an initial rating of EF-1, packing top winds of 112 miles per hour.
The twister knocked down trees and ripped up a gas main in University City, but there were no injuries, University City Mayor Shelley Welsch reported via Twitter. St. Louis County officials said about 100 homes had been damaged.
In addition to St. Louis, cities from Houston to Indianapolis faced a high risk of tornadoes through Thursday night, while some parts of the Midwest could see up to 5 inches of rain, the weather service reported.
Thursday is the 40th anniversary of the "super tornado" outbreak of 1974, when 148 twisters killed 330 people across 13 states.