A former member of the US Air Force who was discharged for assault has been identified as the man who killed at least 26 people and wounded many others at a Baptist church in the small Texas town of Sutherland Springs.

The gunman, identified as 26-year-old Devin Kelley, entered the small church and opened fire with an assault rifle at the congregation attending the Sunday morning service (local time).

The ages of the victims ranged from 5 to 72.

According to US media reports, the gunman had a history with high-powered weapons and had served in logistics readiness at a base in New Mexico from 2010 until his discharge, according to chief of Air Force media operations Ann Stefanek.

Kelley was court-martialed in 2012 for two counts of Article 128 of the Uniform Code of Military Justice, assault on his spouse and assault on their child.

He was sentenced to 12 months’ confinement and received a “bad conduct” discharge in 2014.

Governor Greg Abbott confirmed the death toll and said it was the worst mass shooting in Texas’ history.

“We don’t know if that number will rise or not, all we know is that’s too many, and this will be a long, suffering mourning for those in pain,” he said.

“We ask for God’s comfort, for God’s guidance and for God’s healing for all those who are suffering.”

"As a state we're dealing with the largest mass shooting in our state's history," Texas Gov. @GregAbbott_TX says. pic.twitter.com/TNZgs1YKGq

— CBS News (@CBSNews) November 5, 2017

There was no indication of the gunman’s motive.

According to Texas Department of Public Safety, Freeman Martin, if it were not for a local resident who confronted the gunman, the shooting could have claimed even more lives.

The man, who lives next to the church, reportedly grabbed his own rifle and engaged the shooter, before chasing the gunman from the scene.

“The suspect dropped his rifle, which was a Ruger AR assault-type rifle and fled from the church,” Mr Martin said.

When police found the suspect’s vehicle a short time later, he was found dead as the result of a bullet wound.

“At this time, we don’t know if it was a self-inflicted gunshot wound, or if he was shot by the local resident,” Mr Martin said.

Associated Press quoted an investigator as saying Kelley lived in a suburb of San Antonio, Texas, and did not appear to be linked to organised terrorist groups.

Mr Martin said investigators were looking at social media posts Kelley may have made in the days before the attack, including one that appeared to show a semi-automatic weapon.

‘Our hearts are broken’: Trump

US President Donald Trump, who is in Japan as part of a 12-day tour of Asia, called the shooting an “act of evil” and “horrific”.

“This act of evil occurred as the victims and their families were in their place of sacred worship,” Mr Trump told a media conference.

“We cannot put into words the pain and grief we all feel and we cannot begin to imagine the suffering of those who lost the ones they loved. Our hearts are broken.”