The American state of Arkansas is preparing for an "unprecedented" event like never before - to execute eight death row inmates in just 10 days.

After nearly a dozen years without an execution, Arkansas has adopted the "unprecedented" timetable because one of the three ingredients in the lethal injection will soon expire, according to news.com.au.

Last month, Governor Asa Hutchinson set about scheduling the executions of eight death row prisoners all convicted of murder.

Double executions will be held on four nights over a 10-day period from April 17.

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If carried out, the executions would make Arkansas the first state to execute that many inmates in such a short time since the death penalty was reinstated by the US Supreme Court in 1976.

The state's hurried method poses a number of risks, experts say, with preparations shrouded in secrecy.

Some view the move as odd for Arkansas; after all, only 27 people have been executed in the state since 1990 and because of "drug shortages and challenges to its lethal injection procedures, the state has not carried out an execution since 2005", according to the Death Penalty Information Centre.

The centre claims scheduling two executions on the same day is also unusual.

States have executed two or three inmates on the same day just 10 times in the past 40 years, and no state has ever carried out more than one double execution in the same week.

Oklahoma attempted to do so on April 29, 2014, but called it off after the botched execution of Clayton Lockett earlier that night, where witnesses described a scene from "a horror movie".

The execution made world headlines after the convicted killer took 43 minutes - instead of the usual 10 - to die from a lethal injection using an untested cocktail of drugs that had not been previously used in the United States.

While Texas has executed eight people in a month - twice in 1997 - no state in the modern era has executed that many prisoners in 10 days.

The unconventional execution spree has a morbidly twisted reason; the Death Penalty Information Centre revealed "the hurried schedule appears to be an attempt to use the state's current supply of eight doses of midazolam, a sedative which makes up one third of the execution drug, which will expire at the end of April".

Lockett's prolonged death occurred after the decision to pump the drugs into his body via femoral artery backfired and the product, midazolam, began leaking into his body tissue rather than into his veins.

Arkansas has had a particularly difficult history with lethal injection since 2005 after capital punishment was suspended due to the difficulty in acquiring the lethal drugs required to execute.

The problem with lethal injection

"The stress on the prison and medical staff will be increased, and the risk of making mistakes is multiplied," said Dale Baich, an assistant federal public defender who witnessed inmate Joseph Rudolph Wood's slow death in Arizona in 2014.

"This along with using a drug that has been used in numerous botched executions should make the prison officials in Arkansas very nervous."

Wood's 2014 execution renewed debate over the death penalty and the efficacy of lethal injection. It was the third execution to go awry in the US that year.

Records released to Wood's attorneys show he was administered the sedative midazolam and the painkiller hydromorphone in 50-milligram increments 15 times, for a total of 750 milligrams of each drug. He was pronounced dead after gasping more than 600 times while he lay on the table.

"Those are pretty staggering amounts of medication," said Karen Sibert, a longtime anaesthesiologist and spokeswoman for the California Society of Anesthesiologists.

Sibert, an associate professor at Cedars-Sinai Medical Center, said patients who are sedated before a surgery typically receive no more than 2 milligrams each of midazolam and hydromorphone.

"It would be rare that I would use more than 2 milligrams even for a lengthy surgery," Sibert said. "If that is accurate, that is absolutely a lethal dose."

At the heart of the rush is the shortage of the sedative midazolam, which is used to put an inmate to sleep before receiving the lethal chemicals.

The Arkansas supply expires at the end of April, and it's unclear whether the state will be able to find more.

Arkansas has had trouble obtaining the three lethal drugs it needs to put the men to death, drug makers have stopped selling it to US prisons because they object to their products being used in executions.

To address its trouble, Arkansas now extends secrecy to anyone involved in supplying drugs.

A lawsuit filed Thursday by a Little Rock lawyer contends Arkansas is violating the law by refusing to release documents proving they acquired three lethal drugs from legitimate sources.

The Arkansas Department of Correction used to release package inserts accompanying vials of the deadly drugs but says it no longer will do so because The Associated Press in 2015 used their distinct design to unmask the manufacturers.

When asked what assurances the agency can give the public about its preparations, spokesman Solomon Graves said: "We are implementing procedures consistent with all applicable state law."

The lack of information is part of a trend among states to keep more execution details out of public view and less vulnerable to challenges from opponents.

"As states had more and more problems in carrying out executions, their response has not been to fix the problems but to hide behind secrecy to prevent those problems from being disclosed," said Robert Dunham, executive director of the Death Penalty Information Centre.

Correction Department Director Wendy Kelley has declined to discuss the preparations.

Death witnesses needed

But Arkansas has hit an unexpected snag; there are not enough people willing to watch these prisoners die.

According to the New York Times, Arkansas has a "state law (that) requires that at least six people witness an execution to ensure that the state's death penalty laws are properly followed".

But finding six volunteers that fit the requirements to watch someone die isn't all that easy.

"Under Arkansas state law, execution witnesses must be at least 21 years old and a resident of the state, cannot have a felony conviction and cannot be related to the death row inmate or a victim in the case," New York Times reports.

Additionally, finding enough people to cover all the executions has prompted Wendy Kelley, the director at the Department of Correction to personally set out to look for her own death squad.

Who did she call? The local Rotary Club.

"You seem to be a group that does not have felony backgrounds and are over 21," Ms Kelley told members of the Little Rock Rotary Club, according to The Arkansas Democrat-Gazette.

"So if you're interested in serving in that area, in this serious role, just call my office."

Members of the club were so perplexed by Ms Kelley's suggestion they initially thought it was a joke, and some members even laughed at the idea.

"It quickly became obvious that she was not kidding," Bill Booker, a Rotary Club member, told KARK-TV.

A spokesperson for Arkansas' Department of Correction told The Arkansas Democrat-Gazette he did not have a "current count" of citizen witnesses who had signed up to the task, but that Ms Kelley was making "informal inquiries to find more volunteers".

- Additional reporting by the Associated Press' Andrew DeMillo.