As the deadline for the 25-year-old's execution passed at 9am, the Melbourne church where Nguyen went to school tolled its bell 25 times - once for every year of his life.

In Singapore and in cities across Australia, there were protest vigils to mark the first execution of an Australian since Michael McAuliffe in Malaysia in 1993.

Forty-five minutes before his execution, Nguyen's twin brother Khoa arrived alone in a taxi in the pre-dawn gloom to be close to where his twin was to die.

In another taxi behind him, close friends of the Melbourne man, Kelly Ng and Bronwyn Lew, arrived with his lawyer Julian McMahon.

Together they walked into the prison's visitor centre, where they were to wait for the execution to be carried out.

"They want to be as close to Van at this time as possible," McMahon said.

Nguyen's mother Kim would, at the time of execution, be praying at a Singapore chapel with well-wishers, he said.

Kim Nguyen and Khoa were yesterday allowed limited contact with Nguyen during their last visit, after officials ruled out a final embrace.

They were told they would be able only to hold hands with Nguyen, but it emerged Kim Nguyen was also able to touch her son's face and hair.

"There was a grille and they were able to hold each others hands. Kim was able at least for some time to touch his face," McMahon said outside Changi Prison this morning.

"She told me she was able to talk to him and touch his hair.

"That was a great comfort to her.

"She is obviously incredibly upset, but she is more prepared than she has been at any time previously."

Nguyen led to the gallows at precisely 6am today local time.

His lawyers said the 25-year-old would likely carry rosary beads, and walk without shackles from his cell to stand on the trapdoor of the gallows before his hanging.

It is understood that a hearse would be sent to Changi Prison to collect his body at about 11am local time (2pm AEDT).

McMahon said prison authorities would hold a coronial inquest. A death certificate would be issued and the body would be identified by Australian High Commission staff.

"The body will taken and prepared for burial in Australia," said McMahon.

As the time for execution came and went, there were emotional scenes outside the prison.

A small group of Singapore activists gathered, holding photos of Nguyen and chanting Indian incantations.

Human rights lawyer M. Ravi said: "What do we get out of this? What do we get out of this murder?"

He was accompanied by the distraught family of Shanmugam Murugesu, the Singapore drug trafficker who was hanged last May and who had become a friend of Nguyen.

Shanmugam's mother, Letchumi, wailed: "Who is going to help me?"

Earlier, in a cafe nearby, other Singaporean opponents of the death penalty also held a protest vigil.

The newly-formed Singapore Anti-Death Penalty Committee said in a statement they "utterly deplore and condemn" the hanging of Nguyen, as an "inhumane and barbaric punishment disproportionate to his crime".

Members of the group, including artists and professionals, gathered at a 24-hour sidewalk cafe near Changi Prison, lighting a candle atop an outdoor table on which pictures of Nguyen and messages of sympathy were displayed.

Candles were also left at the gates of the prison, where foreign and local journalists camped out next to a television transmission dish.

The vigil was held after Singaporean Prime Minister Lee Hsien Loong said there would be no pardon for Nguyen, caught three years ago at Changi Airport carrying nearly 400 grams of heroin while in transit from Cambodia to Australia.

Candelight and prayer vigils were also held in major Australian cities to mark Nguyen's death and to protest against the death penalty.

In Melbourne, the bells of St Ignatius Catholic Church, Richmond - where Nguyen went to school as a child - rang 25 times to mark every year of his life.

Hundreds of supporters gathered at the church, including former Iraqi hostage Douglas Wood, who twice entered the church before driving away.

Also in Melbourne, more than a hundred lawyers gathered on the steps of Melbourne's County Court to observe a minute's silence.

Supporters of Nguyen gathered outside Singapore High Commission in Canberra, carrying banners reading "Singapore, how could you?", "Thou shalt not kill", and "The bell tolls and we are all diminished".

In Sydney, a vigil was under way in Sydney's Martin Place.

Nguyen's body will be returned to Melbourne at the weekend ahead of his funeral, expected next week

reported by AAP