Twenty-six people have been shot dead in a small Texan church in what the state's governor described as "the largest mass shooting in the state's history".

Key points: US media name gunman as 26-year-old Devin Patrick Kelley

US media name gunman as 26-year-old Devin Patrick Kelley Authorities and local media say he fled the scene but was killed in a neighbouring county

Authorities and local media say he fled the scene but was killed in a neighbouring county Authorities still trying to determine a motive

The shooting occurred at the First Baptist Church in Sutherland Springs in Wilson County, about 65 kilometres east of San Antonio.

The gunman, wearing a bullet-proof vest and carrying an assault rifle, opened fire around 20 minutes after the Sunday morning service was scheduled to start.

Authorities said a civilian with a gun shot at him as he left and chased him away. The gunman was later found dead in his vehicle.

"We are dealing with the largest mass shooting in our state's history," Texas Governor Greg Abbott said.

"The tragedy of course is worsened by the fact that it occurred in a church, a place of worship where these people were innocently gunned down."

Sorry, this video has expired Emergency services converged on the church after the shooting.

Officials did not identify the attacker during a news conference, but two other officials, one a US official and one in law enforcement, who were briefed on the investigation identified him as 26-year-old Devin Kelley.

The US official said Kelley lived in a San Antonio suburb and did not appear to be linked to organised terrorist groups.

The official said investigators are looking at social media posts Kelley may have made in the days before Sunday's attack, including one that appeared to show an AR-15 semi-automatic rifle.

The Pentagon confirmed he previously served in the Air Force, saying he was an airman "at one point".

A Department of Public Safety official said at the news conference that investigators were not ready to discuss a possible motive for the attack.

He said the dead ranged in age from five to 72 years old. Twenty-three were found dead in the church, two were found outside and one died after being taken to a hospital.

Sorry, this video has expired Grief and shock in Sutherland Springs

A 'small, tight-knit church'

More than 100 people gathered after dark on a grassy street corner within sight of the church for a prayer vigil.

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Attendees, including Mr Abbott, lit candles while some wept and others hugged.

They could see the church sign lit up and emergency lights flashing.

Mike Gonzales, who does not attend the church but lives nearby, said, "the people of this church are wonderful people".

"We're coming together to pray for them and show the world that now, in the midst of darkness, there is light."

Sherri Pomeroy, the wife of the church's pastor Frank Pomeroy, said she had lost her 14-year-old daughter "and many friends" in the Sunday shooting.

Ms Pomeroy said both she and her husband were out of town and trying to get back to Sutherland Springs, outside of San Antonio.

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Local woman Amanda Mosel said her 13-year-old goddaughter was gunned down in the shooting.

"From what I've heard, someone just walked in and started shooting," she told MSN.

Ms Mosel said she "sadly" did not attend church this morning, but the church is one she has attended.

"There's maybe 50 of us," she said.

"It's a small, tight-knit church."

Jeff Forrest, a 36-year-old military veteran who lives a block away from the church, said what sounded like high-calibre, semi-automatic gunfire triggered memories of his four combat deployments with the Marine Corps.

"I was on the porch, I heard 10 rounds go off and then my ears just started ringing," Mr Forrest said.

"I hit the deck and I just lay there."

Sorry, this video has expired Local reporter describes scene outside Baptist church where mass shooting occurred

'Shocked and dismayed'

Emergency services converged on the church in the small town, about 50 kilometres south-east of San Antonio, and helicopters were seen taking victims to hospitals.

Megan Posey, a spokeswoman for Connally Memorial Medical Centre, which is in Floresville and about 16 kilometres from the church, said "multiple" victims were being treated for gunshot wounds.

She declined to give a specific number but said it was less than a dozen.

US President Donald Trump, who is in Japan, described the shooting as an "act of evil" and promised his administration's full support for the investigation.

Speaking to US and Japanese business leaders in Tokyo, Mr Trump expressed his sorrow over the "horrific shooting" at a "place of sacred worship".

"Our hearts are broken but in dark times — and these are dark times — such as these, Americans do what they do best," he said.

Texas Governor Greg Abbott issued a statement, describing the shooting as a "horrific 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."

Investigators work at the scene of the shooting. ( AP: Austin American-Statesman/ Jay Janner )

Sutherland Springs is in a rural corner of South Texas where communities are small and tight-knit.

The area is known for its annual peanut festival in nearby Floresville, which was most recently held last month.

"We're shocked. Shocked and dismayed," said state senator Judith Zaffirini, a Laredo Democrat whose district includes Sutherland Springs.

"It's especially shocking when it's such a small, serene area. These rural areas, they are so beautiful and so loving."

Two women embrace after the shooting. ( AP: Austin American-Statesman/Nick Wagner )

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