A witness said the gunman was dressed in what looked like combat gear when he burst into the church and began shooting during the Sunday morning service.
A spokeswoman for Connally Memorial Medical Center in nearby Floresville told Fox News that "we have accepted a number of patients from the shooting".
Federal law enforcement swarmed the scene to offer assistance, including ATF investigators and members of the FBI's evidence collection team.
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"We heard several shots and we all started running inside the store", said the woman, who said she is 49 but declined to give her name. He said he is on his way to Sutherland Springs to meet with families, local, state and federal officials.
It comes just over a month after Stephen Paddock killed 58 people by opening fire on a concert in Las Vegas from his hotel room.
President Donald Trump said he was monitoring the situation while in Japan on a 12-day Asian trip.
CT will update this post as more details become available. Abbott's communications director tweeted that the governor is headed to Sutherland Springs for a briefing and media availability.
There is a large police presence at the church in Sutherland Springs, which 48 kilometres southeast of San Antonio.
A sheriff's department dispatcher said everyone was at the scene and unavailable to comment.