The worshippers were killed at the First Baptist Church in Sutherland Springs, a small rural community about 30 miles (50 kilometers) southeast of San Antonio, reports said.
Wilson County Commissioner Albert Gamez Jr. told AFP there were multiple fatalities and multiple people wounded, but he could not officially confirm the number. With details rapidly unfolding, some unnamed officials were quoted in media reports citing tolls as high as 27 dead and 20 or more wounded.
The shooter reportedly walked into the church shortly before noon - at a morning service that witnesses said was normally attended by some 50 people - and opened fire. A two-year-old was among the wounded, the Dallas Morning News website reported. A spokeswoman for Connally Memorial Medical Center in nearby Floresville told Fox News that "we have accepted a number of patients from the shooting." She gave no number.
Federal agents arriving
A witness working at a gas station across the street said he heard at least 20 shots being fired in quick succession, CNN reported. Others nearby said the shooter appeared to have reloaded more than once.
Emergency personnel rushed to the scene, and some victims were evacuated by helicopter.
Copyright Agence France-Presse, 2017