Asylum seekers are being transferred from Darwin's Wickham Point detention centre as the government prepares to close the facility.
The Department of Immigration and Border Protection announced earlier this year the lease for the centre would not be renewed beyond November 2016.
Natasha Blucher, from the Darwin Asylum Seeker Support and Advocacy Network, said groups of detainees had been transferred out Wickham Point regularly since June.
"Tomorrow – as far as we understand – is the last transfer of asylum seekers," she said.
"There are around 16 people left and they’ll go tomorrow.”
The Department did not confirm the date of closure but a spokesman told SBS in a statement that it was "taking appropriate steps to prepare, including planning and undertaking the transfer of current detainees at Wickham Point who will remain in immigration detention after the closure".
The spokesman would not reveal where the detainees were being moved to.
"For operational reasons we are unable to provide details on individual transfers or detention placements," he said.
Ms Blucher said she understood most of the detainees were being sent to the Yongah Hill facility in Western Australia or the Melbourne Immigration Transit Accommodation (MITA) facility in Melbourne.
Immigration Minister Peter Dutton made the announcement that Wickham's lease would not be extended ahead of the May budget this year.
He also announced that three other facilities would close, including the Maribyrnong detention centre in Victoria, the Blaxland compound at Villawood detention centre in Sydney and Perth residential housing.
The announcement was met with disappointment by NT Chief Minister Adam Giles.
"Darwin is the frontline of defence of northern Australia and at the time when the federal government is closing detention centres around this nation they must keep the Darwin detention centre open," he at the time.
"If the federal government pursue this agenda of wanting to remove the detention centre out of Darwin and either putting it down south or in another position, I think it leaves Australia pretty bare with facilities to be able to meet the need of any likely future illegal arrival that may turn up on our shores."
Erina Early, Secretary of the NT branch of United Voice - the union that represents workers at Wickham Point - told SBS the closure would have a big impact on workers.
"It is quite upsetting because there are going to be 300 employees unemployed," she said.
Related reading
We don't want to come to Australia: asylum seekers on Nauru
Ms Blucher said advocates had supported the initial announcement but were somewhat disappointed at how it was being carried out.
"As much as we like to see detention centres close, it’s starting to feel like this closure is a bit of an election stunt in that people are getting packed into detention centres elsewhere rather than more releases happening," she said.
Ms Blucher said being moved from Darwin had different implications for different detainees.
"For some people it’s better if they go to MITA [in Melbourne] because they’re in a city, there’s more of their community members there," she said.
"A lot of people have family and friends in some of the other cities and we have seen a couple of successes where people are returned to centres close to their families or their kids or their wives, but for some people they have been transferred further away from their kids".
Earlier in the year, the Human Rights Commission that found "concerning evidence about the mental and physical health" of children held at Wickham Point.
Paediatricians Professor Elizabeth Elliott and Dr Hasantha Gunasekera visited the facility in October 2015 and interviewed 69 families there.
"These children, most of whom had spent months in Nauru, are among the most traumatised [Dr Gunasekera and I] have ever seen in our 50 years of combined professional experience," Professor Elliott said.
