Indonesia's method of execution has remained unchanged since 1964. This weekend will mark the first executions of Indonesia's death row prisoners for 2015. The government has announced that 20 are scheduled for the year.

Australians Myuran Sukumaran and Andrew Chan of the Bali Nine face the death penalty. Sukumaran's appeal for clemency was rejected by Indonesian president Joko Widodo.

Chan has yet to hear if his clemency bid is successful, but, if it fails, it is understood he will be put to death at the same time as Sukumaran.

It is not entirely clear when Indonesia has scheduled their executions, but they could take place within months.

The following is a summary of the Indonesian system of executions using firing squads:.

Who will be executed?

At midnight on Saturday local time six prisoners, including five foreigners, were scheduled to be the first executions in Indonesia this year.

Those to be executed are Rani Andriani, from Indonesia, Marco Archer Cardoso Moreira, 52, from Brazil, Tran Thi Bich Hanh, 37, from Vietnam, Namaona Denis, 48, from Malawi, Daniel Enemuo, 38, from Nigeria and Ang Kiem Soei, who was born in Papua but whose nationality is Dutch.

Last month Mr Widodo said a total of 64 prisoners who were sentenced to death in drugs cases would have their clemency applications rejected.

These 64 official killings were necessary, he said, because Indonesia was in "a state of emergency on drugs" with people dying daily.

How will they be executed?

Death sentences in Indonesia are carried out by firing squad.

The six are scheduled to be shot dead in separate isolated grassy areas by simultaneous firing squads of 12 executioners from the paramilitary forces BRIMOB.

In the Indonesian system a white shirt is placed on the convict. They are walked to the execution site by a priest or cleric and given three minutes to calm down.

The prisoner is blindfolded and asked if they wish to stand, sit or kneel. A doctor will place a mark on the shirt above the heart. After the final check is completed the commander will yell: "Do it", to 12 executioners standing within a five to 10 metre range.

Only three will have live ammunition while the rest will fire blanks.

If the prisoner is still alive, the commander will fire the last shot by pressing the barrel of the gun above the prisoner's ear.

The executions will be conducted simultaneously, "because of psychological consideration...so we don't wait one after the other," said Indonesian Attorney General H.M. Prasetyo.

Central Java police have prepared 84 executioners.

Where will the execution take place?

More than three days before the execution the inmates are transported to Nusa Kambangan Island, often described as Indonesia's Alcatraz. Nusa Kambangan is situated off the southern coast of Java and was established as a prison island by the Dutch. It is home to several maximum security prisons.

The island location was described by Attorney General Prasetyo as "an ideal place for the execution."

In the lead up to the executions on Sunday the seaport and the surrounding waters of the island have been regularly patrolled. Only prison wardens and relatives of the prisoners have been allowed to enter the area. Police personnel and officers from the Attorney General's office have been deployed to maintain security in and around the island.

What is Indonesia's history of execution?

Indonesia's method of execution has remained unchanged since a decree signed by its first president, Sukarno, in 1964. The enthusiasm with which it is applied has waxed and waned over the 50 years since, but from his early talk, the seventh President, Joko Widodo, seems likely to be a strong supporter of the policy.

The last public polls on the subject showed in 2006 that 76 per cent of people supported executing drug traffickers – significantly higher than those calling for murderers to be shot – and that figure may since have risen alongside the rise in drug use.