The shooting occurred about 11:20 a.m.at the West Freeway Church of Christ in the Fort Worth suburb of White Settlement and was captured on the church's live stream of the service, officials said.
One person died at the scene and one person died on the way to the hospital, MedStar spokeswoman Macara Trusty told the Dallas Morning News.
The Fort Worth Fire Department said three people, including the person who they believed to be the shooter, were transported from the scene in critical condition.
Video of the scene from CNN affiliate KTVT showed several agencies present - including Fort Worth Police, Fort Worth Fire Department and MedStar EMS. Also assisting are agents with the Bureau of Alcohol, Tobacco and Firearms.
Witnesses told the news outlet that the gunman walked up to a server during communion and opened fire with a shotgun. It said church members can be heard screaming and crying.
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"It was the most scariest thing".
It is not the first deadly shooting to take place at a church in Texas.
A gunman has killed one person and critically injured another inside a packed Texas church during a livestreamed service before he was shot dead by an armed member of the congregation.