A gunman fatally shot two people before parishioners shot and killed him at a church near Fort Worth, Texas, on Sunday, authorities said.

J.P. Bevering, police chief of White Settlement, in Tarrant County, said the man opened fire at West Freeway Church of Christ during services shortly before noon. Worshipers returned fire, killing the gunman, Bevering said.

One person was pronounced dead shortly after the shooting. Another parishioner who was in critical condition later died, authorities said.

One of them was identified by his daughter as Anton “Tony” Wallace, 64.

"We lost two great men today," Britt Farmer, the church's senior minister, told reporters late Sunday. "But it could've been a lot worse."

Bevering said the shooter, who has not been identified, appears to have walked into the church and sat down.

"He got up, pulled out a shotgun and fired it at a parishioner," Bevering said. "That parishioner is deceased."

The shooter struck a second person before two other parishioners, who are volunteer members of a church security team, returned fire. The shooting was over within six seconds, Lt. Gov. Dan Patrick told reporters.

They "drew their weapons and took out the killer immediately, saving untold number of lives," Patrick said.

Matt DeSarno, the special agent in charge of Dallas' FBI field office, said investigators were still trying to determine the motive behind the shooting.

DeSarno described the shooter as a "relatively transient" person with roots in the area who'd been arrested multiple times in different cities. He declined to provide additional details.

Download the NBC News app for breaking news

Anton Wallace’s daughter, Tiffany Wallace, who witnessed the shooting, described the gunman as a white man with a fake beard and black hair who was wearing a trench coat.

“I was thinking, hey, he’s a visitor probably looking for a new church home,” she said.

Moments later, she said, the man stood up and fired at a security guard and two other parishioners, including her father, a registered nurse at Texas Health Harris Methodist Hospital Fort Worth who regularly attended West Freeway.

“I ran towards my dad, holding him,” she said. “I told him I love him.”

Her family was left reeling over the loss. If the gunman had needed food or shelter, she said, the church would have provided it.

“Whatever he needed, he didn’t need to take an innocent life — our dad, grandfather, husband, father, fixing to be father-in-law,” she said. “He was just our rock.”

Fort Worth police Sgt. Christopher Daniels said that a video of the service streamed online earlier Sunday may have documented the attack but that it was removed from YouTube.

Farmer confirmed the video's existence to NBC News.

Gov. Greg Abbott called the shooting an "evil act of violence" in a statement Sunday afternoon.

"Places of worship are meant to be sacred, and I am grateful for the church members who acted quickly to take down the shooter and help prevent further loss of life," Abbott said.

White Settlement was given its name in the 1800s by Native Americans after non-Indigenous families began to settle in the area, according to the city's website.