A Tennessee death row inmate remained in critical condition in hospital after surviving two attempts to execute her by lethal injection, prompting Governor Bill Lee to halt all executions in the state for the rest of the year.

Christa Pike, 50, was given two lethal doses of pentobarbital on Wednesday but remained alive, according to her lawyers. She was subsequently taken to hospital by ambulance and was receiving life-saving treatment.

Pike was sentenced to death in 1996 for the murder of 19-year-old Colleen Slemmer, whom she was convicted of beating, torturing and killing along with her then-boyfriend, Tadaryl Shipp. Pike was 18 when the crime took place.

Lawyers Seek Commutation After Failed Execution

"We don't have a sense of her prognosis or much update on her health at the moment," Pike's lawyer Randy Spivey told reporters on Thursday. "But we do know that she is alive right now."

Her legal team is now seeking to have her death sentence commuted. Spivey said the governor should commute Pike's sentence, a request that had previously been rejected.

The attempted execution became the subject of a last-minute legal battle before the US Supreme Court ultimately allowed the lethal injections to proceed.

Slemmer's mother, May Martinez, had supported the execution and travelled to Tennessee to witness it. Speaking to NBC News after the failed attempt, she described what happened as "a mess".

Lawyer Describes Hour-Long IV Struggle

Pike's lawyers provided further details on Thursday about what they described as a harrowing execution attempt that took place largely behind a curtain and away from observers.

"Last night, the execution team attempted to establish an IV line for an hour," Spivey said. He said he counted at least seven needles being used in Pike's left arm, including one that appeared to be bent when it was removed after an unsuccessful attempt.

Spivey said observers were kept in a dark room behind a closed curtain after the second lethal dose had been administered. He said it became clear within minutes that Pike was still breathing.

"No-one knew what was going on behind that curtain," Spivey said. "I had no idea when and if medical professionals began to assist."

Tennessee Orders Independent Review

Another member of Pike's legal team, Stephen Ferrell, said the lawyers were considering other legal options while focusing first on Pike's recovery.

"We want to think this through and we want to make sure that Christa recovers and has some input in what she wants," Ferrell said.

Governor Bill Lee has ordered an independent review of the failed execution. On Thursday, he said the investigation would be "thorough" and warned that it "is going to take time".

The governor's decision to halt executions for the remainder of the year follows an attempt that left Pike alive and requiring hospital care.