Nine drug traffickers held emotional farewell meetings with their families at an Indonesian prison on Tuesday, after Jakarta rejected last-ditch pleas from around the world for clemency and ordered their mass execution to proceed within hours.

"I won't see him again," said Raji Sukumaran, the mother of an Australian who will go before a firing squad along with a fellow countryman and convicts from Nigeria, Brazil, the Philippines and Indonesia.

"They're going to take him at midnight and shoot him. I'm asking the government not to kill him. Please don't kill him today," she told reporters, weeping as she spoke.

Hundreds of people began gathering in cities across Australia for vigils for Myuran Sukumaran and Andrew Chan, holding placards and calling for Australia to respond strongly to its neighbor if the executions proceed.

The death penalties have been condemned by the United Nations, and strained ties between Australia and Indonesia.

Security at the high-security prison on an island off the Central Java coast was heightened on Tuesday. Religious counselors, doctors and the firing squad were alerted to start final preparations for the execution, and a dozen ambulances, some carrying white satin-covered coffins, were seen arriving.

Amid chaotic scenes outside the jail, a member of one of the Australian's family collapsed and was carried through the crowd.

"I saw today something that no other family should ever have to go through. Nine families inside a prison saying goodbye to their loved ones," said Chan's brother, Michael. "It's torture."

TWELVE MARKSMEN FOR EACH PRISONER

Indonesian authorities have declined to specify a time for the executions, which are due to take place at a nearby clearing in a forest, but the last time a group of drug traffickers were executed earlier this year it was carried out at midnight.

The prisoners will be given the choice to stand, kneel or sit before the firing squad, and to be blindfolded. Their hands and feet will be tied.

Twelve marksmen are assigned to fire at the heart of each prisoner, but only three have live ammunition. Authorities say this is so that the executioner remains unidentified.

Philippine President Benigno Aquino said on Tuesday that he had made one last appeal to the Indonesian government to spare a Filipina among the nine, arguing that she could be a vital witness in prosecuting drug syndicates.

"She does present an opportunity right now to be able to uncover all the participants and start the process of bringing them to the bars of justice," Aquino told reporters in Malaysia, where he was attending a meeting of Southeast Asian leaders.

Mary Jane Veloso, a mother of two, was arrested in 2010 after she arrived in Indonesia with 2.6 kg of heroin hidden in her suitcase.

Veloso's lawyers filed a human trafficking complaint recently against another Filipina, Maria Cristina Sergio, who they allege promised the death-row inmate a job as a domestic worker in Indonesia but instead led her to become a drug mule.

Sergio voluntarily surrendered to police in the Philippines on Tuesday, seeking protection after receiving death threats via her social media accounts and mobile phone.

"I'd say it's a changing alibi," Indonesia's attorney-general, HM Prasetyo, told reporters.

"Now she says she's a victim of human trafficking. I think these are just efforts to delay the execution. We have given her all legal avenues. Don't force us to change. If we're not firm, it means we're weak in the war against drugs."

Filipino boxing superstar Manny Pacquiao, who is in the United States for a title fight, made a televised appeal to Indonesian President Joko Widodo on behalf of his countrywoman, Veloso: "I am begging and knocking on your kind heart that your excellency will grant executive clemency to her."

AUSTRALIA: "THERE WILL BE CONSEQUENCES"

Authorities on Monday granted Australian Chan's last wish, which was to marry his Indonesian girlfriend at the prison.

But they rebuffed last-minute appeals from Australia to save the lives of Sukumaran and Chan, who were arrested in 2005 as the ringleaders of a plot to smuggle heroin out of Indonesia.

The pending executions have strained Indonesia's relations with Australia, Nigeria and Brazil, which will likely worsen after the death sentences are carried out.

Australian Foreign Minister Julie Bishop told ABC television: "Should these executions proceed in the manner that I anticipate, of course, there will have to be consequences."

Australia-Indonesia relations have been tested in recent years by disputes over people smuggling and spying. In late 2013 Indonesia recalled its envoy and froze military and intelligence cooperation over reports that Canberra had spied on top Indonesian officials, including the former president's wife.

Indonesia has harsh punishments for drug crimes and resumed executions in 2013 after a five-year gap. Six have been executed so far this year.

Widodo's steadfastness on the executions, which has strong public support at home, stands in contrast to a series of policy flip-flops since he took office six months ago. Palace insiders and government officials portray him as sometimes out of his depth and struggling to get around entrenched vested interests.