The mass shooting was reported at First Baptist Church of Sutherland Springs, which is about 30 miles southeast of San Antonio. The gunman has been fatally shot by police.
Paxton told Fox News that, based on reports, up to 27 people and "many more" wounded when a man walked into the church around 11:30 a.m. on Sunday and opened fire at the crowd of people.
Emergency personnel respond to a fatal shooting at a Baptist church in Sutherland Springs, Texas, Sunday, Nov. 5, 2017. (KSAT via AP)
If the number of people dead is confirmed, Sunday's shooting would be the deadliest at a church in modern U.S. history.
Rep. Henry Cuellar told Fox News that investigators believe the gunman drove to the church from Comal County, Texas. He did not name the shooter.
"It is horrible," Wilson County Commissioner Larry Wiley told Fox News of the massacre, the motive of which is unknown. "It appears someone walked in and started shooting."
The church's pastor, Frank Pomeroy, said his 14-year-old daughter was killed in the shooting, according to ABC News.
"We have accepted a multiple number of patients from the shooting," Megan Posey, a spokeswoman for Connally Memorial Medical Center in Floresville, 15 miles from church, told Fox News. She said she did not have a specific number. She said doctors were assessing the patients.
Some victims were transported to Brooke Army Medical Center in San Antonio, KSAT reported.
Helicopters and emergency personnel were seen arriving at the scene. The FBI is also on scene.
The gunman, according to Wiley, was killed roughly five miles away in Guadalupe County after being cornered by deputies.
Law enforcement officials stand next to a covered body at the scene of a fatal shooting at the First Baptist Church in Sutherland Springs, Texas, on Sunday, Nov. 5, 2017. (Nick Wagner/Austin American-Statesman via AP)
Texas Attorney General Ken Paxton told Fox News that "people never think" a shooting like this can "happen in their communities."
"In a small town, ... I can imagine that these people are devastated. And everyone in the community is going to ... have some type of close relationship" to those either killed or injured at the First Baptist Church.
"This is horrific for our tiny little tight-knit town," Alena Berlanga, who lives 10 minutes outside of Sutherland Springs told The Associated Press. "Everybody's going to be affected and everybody knows someone who's affected."
President Trump, who's currently traveling in Asia, tweeted: "May God be w/ the people of Sutherland Springs, Texas. The FBI & law enforcement are on the scene. I am monitoring the situation from Japan."
Texas Governor Greg Abbott said in a statement that "While the details of this horrific act are still under investigation, Cecilia and I want to send our sincerest thoughts and prayers to all those who have been affected by this evil act."
"I want to thank law enforcement for their response and ask that all Texans pray for the Sutherland Springs community during this time of mourning and loss," the statement read.
Sutherland Springs has a population of about 400 residents.
Sunday's shooting comes just over a month after 58 people were killed and hundreds injured on Oct. 1 after a gunman opened fire on a country music festival in Las Vegas.
