A court-martialled former US Air Force airman armed with a powerful assault rifle sprayed bullets on worshippers at a Sunday service at a rural church in Texas, killing at least 26 people, including 12-14 children, in the latest act of gun violence to shock America.

Investigators believe the suspect, identified as 26- year-old Devin Patrick Kelley, suffered a self-inflicted gunshot wound.

Officials have now said the shooting inside the small South Texas church was not racially or religiously motivated, noting a ‘domestic situation’ within the suspect’s family.

The Sunday massacre at the First Baptist Church in Sutherland Springs, about 40 miles southeast of San Antonio, also left 20 people injured and sent shockwaves across the country.

The ages of the deceased range from 18 months to 77 years, authorities said this morning.

Some parents had shielded their children with their bodies, Wilson County Sheriff Joe Tackitt said.

When Tackitt arrived at the church, he added, first responders were doing triage and almost everyone was covered in blood.

The gunman opened fire at the First Baptist Church in Sutherland Springs yesterday, killing 26 people and wounding about 20 others, officials said.

Kelley, wearing black tactical-style gear walked into the First Baptist Church in Sutherland Springs and started firing from an assault rifle just after the Sunday morning service began, officials said.

Among the dead were 12 to 14 children, Tackitt told reporters. 20 other people were also injured in the attack.

A pregnant woman and the pastor’s 14-year-old daughter were also among the dead.

Police have identified all but one of the deceased.

Nearly everyone in the church at the time of the shooting had some type of injury, the Sheriff said.

Investigators worked through the night, and are still on the scene of the deadly shooting this morning trying to piece together exactly what happened.

Texas Governor Greg Abbott called the slaughter “the largest mass shooting” in the state’s history and ordered flags across the state to fly at half-staff.

Authorities confirmed that the church shooter was a heavily-armed white male, in his 20s, but refused to name him. But the media identified the gunman as Kelley, who was discharged from the US Air Force in 2014.

Police said the gunman crossed the street in his vehicle, got out and began firing from his rifle. He then moved to the right side of the church, continuing to fire and then into the building.

As he left, he was confronted by a resident who grabbed his rifle and then began to fire at him as he fled. He then chased the shooter who left the scene in his vehicle before leaving the road at the border with Guadalupe County.

He was found dead inside the vehicle, although authorities are not sure if the shooter died from a self- inflicted wound, or whether it was from the resident.

“The exact circumstances of the gunman’s death are still under investigation,” the Texas Department of Public Safety said.

The San Antonio FBI branch said there was no indication of the gunman’s motive. But investigators say Kelley’s in-laws attended the church at times but were not at the service yesterday morning. It’s not clear if he targeted the church, nearly 48 kms from San Antonio, because of this connection.

In a brief statement, the Pentagon said the suspect was an airman “at one point,” but additional details about his time in the Air Force were not immediately available.

The US officials said the suspect lived in a San Antonio suburb and does not appear to be linked to organised terrorist groups. The officials said investigators are looking at social media posts Kelley may have made in the days before the attack.

Kelley was previously a member of the US Air Force and served at Holloman Air Force Base in New Mexico from 2010 until his discharge, according to Air Force spokeswoman Ann Stefanek.

He was court-martialled in 2012 for assault on his spouse and their child, according to Stefanek. He served a year in confinement and received a bad conduct discharge, the spokeswoman said, adding his rank was also reduced.

President Donald Trump, who is in Japan on the first leg of a 12-day Asia tour, expressed condolences to the victims of the mass shooting and also called Governor Abbott.

He condemned the shooting as an “act of evil” and said Americans would pull together.

“And through the tears and through the sadness, we stand strong, oh so strong,” he said but dismissed the need for guns control.

Trump said the gunman had a “mental health problem” and that this “is not a guns situation”.

“Preliminary reports show a very deranged individual who’s been having a problem for a very long time,” he said, adding that “We have a lot of mental health problems in our country.”

The shooting has devastated the small Texas town in the east of San Antonio, described as a place where “everybody knows everybody” and sent shockwaves across the US, as the nation confronts a breaking point over race and gun violence.

Less than a thousand people live in Sutherland Springs and officials believe that the number of people who are injured and killed make up about four per cent of the entire population.

Former president Barack Obama expressed his condolences over the incident and said, “may God also grant all of us the wisdom to ask what concrete steps we can take to reduce the violence and weaponry in our midst,” he said.

It’s the deadliest mass shooting in Texas history — and the fifth deadliest in modern US history.

The shooting comes just a month after a gunman in Las Vegas opened fire on an outdoor music festival, killing 58 people in the deadliest mass shooting in recent US history.

Texas witnessed its worst shooting in 1991 when a man drove his pickup truck into a cafeteria and opened fire, killing 23 people.