Death-row inmate Christa Pike has been rushed to hospital after surviving two lethal doses during an apparent botched execution on Thursday (AEST) in Tennessee.

The 50-year-old convicted killer’s execution was earlier halted with an hour to go after an eleventh-hour legal stay, but was later given the green light by the US Supreme Court.

When her execution proceeded, her lawyers said Pike had “not lost consciousness and still has a heartbeat and is audibly snoring”.

Execution witnesses were reportedly ushered out of the viewing area when it became apparent she was still alive.

Pike’s lawyers filed an emergency motion in the Tennessee Supreme Court to try and stop the process.

They stated in the filing that Pike had received two syringes filled with lethal chemicals, but she was still alive and experiencing “unnecessary agony”.

The lawyers also issued a public statement saying that the State of Tennessee “once again failed to carry out a lawful execution”.

“We take no pleasure in being right, but the concerns raised by Ms Pike proved to be true: Difficult vein access, blown veins, degraded pentobarbital, no emergency medical care available when things inevitably go wrong, all under a protocol that remains veiled in secrecy.

“Christa is being treated at a nearby hospital,” they continued. “We have not been informed as to her condition.”

It was not clear whether Pike, the first woman to be executed in the state for 200 years, was dead or alive.

State corrections officials put out a late-evening statement saying that they followed “every step” of Tennessee’s “execution protocol” but that it did not immediately kill Pike.

“The lethal injection chemical in the protocol has consistently been effective, and the protocol does not allow for additional procedures beyond what was carried out this evening.

“Christa Pike has been transported to an off-site medical facility.”

Tennessee Governor Bill Lee said all remaining executions this year would be stayed.

“Carrying out a lawfully imposed sentence is among the State’s most serious responsibilities, and the people of Tennessee expect it to be done in a manner that is not only legal and constitutional, but is effective,” Lee said in a statement.

Pike was sentenced to death by lethal injection for murdering a schoolmate three decades ago.

The Tennessee Department of ‌Correction said in a statement earlier on Thursday (AEST) that it was planning “to move forward with the execution today.”

Pike, 50, whose clemency petition highlighting childhood trauma and sexual abuse was denied by Governor Bill Lee on Monday, was also the only person in the modern era to be executed in Tennessee for a crime committed as a teenager.

The Supreme Court lifted ‌a temporary stay ‌of execution that had ⁠been granted by a three-judge panel of the 6th US Circuit Court of Appeals one hour ​before Pike had been scheduled to be put to death.

The appellate panel voted 2-1 to order a “short stay” to allow time to weigh Pike’s claim that evidence of her childhood sexual abuse were not adequately considered during her sentencing.

Pike’s lawyers argued the sentencing should be reopened because the state’s attorneys had conceded in court for the first time, at a hearing in August, that

Pike had suffered from sexual abuse, including rape, as ⁠a child.

But the Tennessee attorney-general’s office immediately asked the US Supreme Court ‌to vacate ​the stay.

And the high court’s decision siding with Tennessee marked the final word on whether the execution was permitted to go forward, so ​long as it took ‌place before her death warrant expired at midnight on Wednesday (US Central Daylight Time).

Pike was 18 in January 1995 when she, ‌a 17-year-old boyfriend and a third companion lured 19-year-old Colleen Slemmer, a classmate at their Knoxville Job Corps vocational centre, into a wooded area where they tortured and killed her.

Trial testimony indicated Pike viewed Slemmer as a rival for the affections of her boyfriend, Tadaryl Shipp.

Pike and Shipp confessed to the killing, and both were convicted the following year of first-degree murder. Pike was sentenced to death, while Shipp received a ​life sentence with the possibility of parole.

Their co-defendant, Shadolla Peterson, who was 18 at the time of the murder and had acted ​as a lookout for the other ⁠two, appeared as a witness for the prosecution and received probation.

-with AAP