A gunman in full combat gear killed 26 people and wounded another during a Sunday service at a small Baptist church in the southern US state of Texas, before he was shot and killed by police, witnesses and officials said.

The shooting spree rocked the First Baptist Church in Sutherland Springs, a small community of about 400 people located about 65 kilometres south-east of San Antonio.

Authorities confirmed 26 people, aged between five-years-old and 72-years-old, dued after the gunman opened fire outside and inside the church. They said a local resident had confronted the gunman who had then left the church and was subsequently killed following a brief chase north into neighboring Guadalupe County.

A witness said the gunman was dressed in what looked like combat gear when he burst into the church and began shooting during the Sunday morning service.

The dead included the 14-year-old daughter of the church's pastor.

Emergency services rushed to the church in the small town and helicopters were seen taking victims to hospitals. A large police presence could be seen at the church.

United States President Donald Trump said on the social media service Twitter from Japan: "May God be with 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 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."

It was one of the bloodiest church attacks in recent memory, though there have been several shooting sprees in the country amid an ongoing debate about the number of firearms available in the United States. The motive of the attacker was not immediately clear but came at a time when this nation is on edge after last week's attack in New York killed eight people and injured more than a dozen.

- with BosNewsLife