A church in Florida has sent out a terrifying warning to potential attackers two weeks after Devin Kelley walked into a Texas church and took the lives of 25 people and an unborn child when he opened fire with an assault rifle.

In response to the devastating shooting, the River of Tampa Bay Church in Tampa posted a sign with a warning which reads in capital letters: "Please know this is not a gun free zone - we are heavily armed.

"Any attempt will be dealt with deadly force - yes we are a church and we will protect our people." The message is signed 'The Pastors'.

The sign has been hung at each door of the church for about a year, but has only garnered significant attention recently, after Senior Pastor Rodney Howard Browne shared it to his Instagram account.

"It is a deterrent," Pastor Allen Hawes told The Tampa Bay Times this week. "Look at what is going on. In the past two months, look at what happened in Texas. Look at what happened in Las Vegas.

"Because we are a church that is on television, we are very involved in the community. We want people to know that this is a safe zone."

The shooting at a Texas church followed the deadliest shooting in US history, perpetrated by 64-year-old Stephen Paddock, who fired into crowds attending a music festival in Las Vegas, killing 58 and injuring more than 500 others.

"If you walk through the door with the intention to harm, that sign serves as a deterrent to you," Hawes added. "We are not a soft target. People here will defend their families.

"I think just collectively, we pay very close attention. Look at Seminole Heights. Someone is murdering people. This stuff is happening all the time. Do you wait for another shooting to take precautions?"