The Indonesian government has ordered preparations to be made for the executions of two Australian drug smugglers as well as eight others on death row.
Tony Spontana, a spokesman for the Indonesian attorney-general, said the head of General Crimes had issued letters ordering prosecutors to start preparing for the executions.
Mr Spontana said orders were sent on Thursday but it was unclear when the prosecutors would receive them or how quickly the executions could be arranged.
He said the letters were not the final notification that must be given to the condemned inmates.
Indonesian prosecutors will give three days' notice to the men before they face a firing squad.
Indonesia has also asked foreign embassies to go to a maximum security prison ahead of the expected executions, Reuters news agency has reported.
The request was disclosed by foreign ministry officials in Jakarta.
A source at one foreign embassy confirmed representatives had been advised to go to the prison tomorrow.
However, she said the date of the executions was still not known, but they were expected to be within days.
Peter Morrisey, a lawyer for the pair, said while not the 72 hours' notice, the recent development was a worrying sign.
He said the legal process was not yet finished, with both a constitutional court challenge and a judicial commission still in progress.
"That looks as if the attorney-general's office is determined to press ahead and hustle through," Mr Morrisey said.
"That's the zone we're in now. We haven't got the 72-hour knock but that could be imminent.
"He's [the attorney-general] saying that he's going to press ahead, and he's saying that all the legal proceedings are finished and that they've had their go.
"And that's just not the case, there are still two cases there."
Another lawyer for the pair, Julian McMahon, said the families of Chan and Sukumaran were travelling to Indonesia.
"There's one mother in Indonesia and I think the families are all going to be travelling straight away, the ones who aren't already there," he said.
In another sign that plans are underway, Mr Spontana also confirmed that Filipina Mary Jane Veloso, who is due for execution alongside Chan and Sukumaran, will be moved to Nusakambangan today.
Nusakambangan is the island near Cilacap on the south coast of Java, where the Australian pair are being held ahead of the executions.
Veloso, who says she was tricked into carrying luggage containing drugs into Indonesia, has been in a prison in Yogyakarta.
Mr McMahon said Veloso's transfer to Nusakambangan was an indication the executions were imminent.
"If she has been transferred, that is significant because it's difficult for a woman to be kept as a prisoner at the relevant prison where people are taken from to be executed," he said.
Authorities had planned to execute Chan and Sukumaran in February, but it was put on hold until all legal challenges were completed.
The pair were sentenced to death in Indonesia for attempting to smuggle heroin home from Indonesia 10 years ago.
They were denied a chance to have their clemency bids reviewed and the Indonesian government said they had run out of legal options.
On Tuesday, Indonesia's government-owned news service Antara quoted president Joko Widodo as saying it was "only a matter of time" before the executions happened.
"When it will be done is no longer a question," he said.
"It is only awaiting the conclusion of all procedures and the legal process, which I will not interfere in."
Earlier this month, the pair's lawyers filed a constitutional court challenge questioning the Indonesian president's process of refusing to pardon them from the death penalty.
The appeal was rejected when three judges from Indonesia's state administrative court said clemency fell under the constitution but not under administrative law, and so was not in their jurisdiction.
Indonesian attorney-general Muhammad Prasetyo told one of the pair's lawyers, Todung Mulya Lubis, the case would not be enough to stop the pair from being executed.