A self-confessed serial killer convicted of murdering his wife and another woman is scheduled to be executed by lethal injection in Florida on Thursday.

James Barnes, 61, who is not seeking to halt his execution, is to be put to death at 6:00 pm (2200 GMT) at Florida State Prison in Raiford.

Barnes was serving a life sentence for the 1997 murder of his wife, Linda, when he confessed to the 1988 rape and murder of Patricia Miller, a 41-year-old nurse.

He was sentenced to death in 2007 for Miller's murder.

Barnes was interviewed by German director Werner Herzog for a 2012 television series called "On Death Row" and confessed to two other murders for which he has never faced charges.

In late July, the Florida Conference of Catholic Bishops urged Governor Ron DeSantis to stay Barnes' execution.

"Mr. Barnes' willing acceptance of death... does not absolve the state from bringing it about," they said in a letter.

"Simply put, no one should be executed in our modern penal system, even if they willingly accept it."

DeSantis, a candidate for the 2024 Republican presidential nomination, has signed Barnes' death warrant and declined to stay his execution.

If it goes ahead, Barnes will be the fifth "Death Row" inmate executed in Florida in 2023.

There have been 16 executions in the United States this year.