Six Australians on death row over their role in the Bali Nine heroin smuggling ring could be put to death by lethal injection rather than firing squad if their final appeals fail.

Indonesia's Attorney-General Abdulrahman Saleh on Thursday said the government was mulling "more humane" lethal injections as the preferred way to carry out death sentences.

Saleh flagged the possible change during the first formal hearing Thursday of Bali Nine member Scott Rush's constitutional challenge to the death sentence he has been handed.

Bali Nine ringleaders Andrew Chan and Myuran Sukumaran have also launched constitutional challenges to their death sentences.

Saleh told the hearing that Indonesia continued to believe in the death penalty, ruling out any move to abandon it.

"The death penalty is of necessity still because the perpetrators don't consider what's right for humanity," Saleh told the court.

"... we've held several meetings with Indonesian doctors' association to use a new method, to request some changes in the law, by using injection.

"Like in the USA, now people are injected so they would get unconscious and then the second injections would be the deadly toxic injection.

"That would be more humane."

Saleh said the existing method was to blindfold convicts and put them in front of six shooters, with just one bullet loaded into the six weapons.

After the shooters fired, a doctor is tasked with checking that the convict is dead. If not, the commander of the shooting squad is responsible for delivering a coup de grace.

The chief of Indonesia's National Narcotics Agency agreed the death penalty could not be abolished.

"The implementation of death sentence in Indonesia is still very much needed, because if it is annulled, (I am) worried that Indonesia's situation going to get worse in terms of narcotics cases," I Made Mangku Pastika told the hearing.

Saleh also said that Rush, and by default Chan and Sukumaran, was not entitled to a constitutional challenge because they were not Indonesian citizens.

He said President Susilo Bambang Yudhoyono had granted him the power to tell the court that Rush "doesn't have the legal standing to request a constitutional challenge regarding the narcotics law" because Rush is Australian.

Saleh told the hearing he would move to stop death row inmates from repeatedly seeking clemency, which he said could happen up to five times.

"I hope it won't happen again in the future ... I am going to regulate this," Saleh said.

Pastika also promised to hasten the execution process in an amendment to Indonesia's current narcotics law, which is still being discussed.

The court is yet to set another hearing date in the case of the Australians.

Rush, Chan and Sukumaran were among nine young Australians arrested in Bali by Indonesian authorities on drug charges in April 2005, following a tip-off from the Australian Federal Police.

©AAP 2007