The gunman responsible for the mass shooting at a small Texas church has been identified as 26-year-old Devin Patrick Kelley, but police are yet to confirm media reports.
Two officials - one a US official and the other in law enforcement - spoke to The Associated Press on the condition of anonymity.
The US official says Kelley lived in a suburb of San Antonio and he doesn't appear to be linked to organised terrorist groups.
Texas Governor Greg Abbott said it was the largest mass shooting in the state's modern history.
“We don’t know if that number will rise or not, but we know that that’s too many and this will be a long, suffering mourning for those in pain,” he told a press conference.
"We are dealing with the largest mass shooting in our state's history," he added.
Exactly five weeks after the worst shooting in modern US history, the latest tragedy prompted an outpouring of condolences, led by US President Donald Trump.
The worshippers were gunned down at First Baptist Church in Sutherland Springs, a small rural community about 50 kilometers southeast of San Antonio.
The gunman 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, according to Mr Martin.
The suspect, armed with an assault-type rifle and a ballistic vest, then fled from the church after a local citizen grabbed a weapon and fired back.
Following a pursuit, the shooter was found deceased in his vehicle by law enforcement. It is unclear how he died.
Of the victims, 23 died inside the church, two were found deceased outside and one transported to a hospital died.
Up to 20 people were transported to hospitals in San Antonio with injuries ranging from minor to severe. The ages of the victims range from five-years-old to 72.
The dead included the 14-year-old daughter of pastor Frank Pomeroy, the church leader told ABC News.
Annabelle Renee Pomeroy "was one very beautiful, special child," her father said.
Frank Pomeroy had been in the neighboring state of Oklahoma at the time of the shooting, and was driving back to Texas after the tragedy.
Other victims included a six-year-old boy named Rylan who was in surgery after being shot four times, his uncle told CBS News.
A spokeswoman for Connally Memorial Medical Center in nearby Floresville said the hospital received eight patients with gunshot wounds. Four were transferred to San Antonio.
Federal agents arriving
A witness working at a gas station across the street told CNN he heard at least 20 shots being fired in quick succession. Others nearby said the shooter appeared to have reloaded more than once.
Emergency personnel rushed to the scene in the community of 400 people, and some victims were evacuated by helicopter.
Police formed a perimeter around the area. Tearful relatives and neighbors stood outside, nervously awaiting news from inside the traditional, white-frame church.
Law enforcement officers man a barricade near the First Baptist Church of Sutherland Springs after a fatal shooting, Sunday, Nov 5, 2017, in Sutherland Springs. Source: AAP
Sutherland Springs in Texas. Source: Google Maps
Agents from the FBI and the Bureau of Alcohol, Tobacco, Firearms and Explosives were heading to Sutherland Springs, the agencies said.
US President Donald Trump on Monday condemned what he described as a "horrific shooting".
"This act of evil occurred as the victims and their families were in their place of worship. Our hearts are broken," Trump said on a visit to Japan.
"We pull together, we join arms ... through the tears and the sadness we stand strong," added the president, addressing business leaders on day two of his Asian trip.
Both US Senator for Texas Ted Cruz and Texas Governor Greg Abbott offered their condolences.
The shooting comes just over a month after a gunman in Las Vegas fired down from a hotel room onto an outdoor concert, killing 58 people and wounding hundreds. It was the deadliest mass shooting in modern US history.
And Sunday's tragedy came just over two years after a white supremacist, Dylann Roof, entered a historically black church in Charleston, South Carolina, and shot nine people to death.
Connecticut Senator Chris Murphy wrote a powerful statement condemning the loose gun laws in the United States.
