A man pulled out a shotgun inside a North Texas church on Sunday and opened fire, killing two people, authorities said. It could have been far worse.

Two congregants, both volunteer members of the church's security team, drew their weapons and confronted the gunman, fatally shooting him and saving an "untold number of lives" at West Freeway Church of Christ in White Settlement, a town of about 17,000 people near Fort Worth.

Their actions, described as "heroic" by the Texas Department of Public Safety, brought a quick end to an attack that remained under investigation on Sunday night. Authorities have not provided information about a possible motive.

Officials have not released the names of the victims or the gunman, whom FBI Special Agent in Charge Matthew DeSarno said had roots in the area but is “relatively transient."

“This team responded quickly and within six seconds, the shooting was over. Two of the parishioners who were volunteers of the security force drew their weapons and took out the killer immediately, saving untold number of lives,” said Texas Lt. Gov. Dan Patrick, who also hailed the state’s gun laws.

“We lost two great men today," Britt Farmer, the church's senior minister said, "but it could have been a lot worse.”

There were more than 240 parishioners in the church at the time of the shooting, authorities said, and the service was being livestreamed to countless homes.