California Governor Gavin Newsom said he was commuting all death sentences across the state to life imprisonment, in a move that will affect almost 550 prisoners.

Newsom, who is widely expected to make a run for the White House in 2028, said capital punishment was "incompatible" with the values of the most populous state in the US.

"Today I am acting on my long and deeply held conviction that individually and collectively we are stronger as a society when we reject state-sanctioned killing," he wrote in a letter addressed "to all Californians".

With 548 people awaiting execution in California, the state has one of the largest death row populations in the world.

However, it has not carried out a death sentence for two decades, even as courts continue to impose the penalty on those convicted of murder and other serious crimes.

"Many Californians feel that those who commit brutal crimes deserve to die. But as governor, I have concluded the state cannot morally kill them," he said, calling the decision "among the most difficult of my career".

"I do, however, pray that this action will finally separate the memories of the victims of these crimes from the fate of those who harmed them. We can now let these offenders die in obscurity while we forever remember and honor their victims."

The announcement comes with a renewed spotlight on the death penalty in the United States, one of the few wealthy countries to retain capital punishment.

Three other US states – Alabama, Florida and Indiana – each carried out executions on the same day as Newsom's announcement.

In September, the state of Tennessee failed twice to kill convicted murderer Christa Pike with a lethal injection before rushing her to hospital.

Last month Defence Secretary Pete Hegseth announced that the firing squad execution of a man who went on a shooting rampage at a US Army base would be livestreamed. (AFP)



Edited by Aaron Tam