The number of detainees at the Christmas Island detention centre has almost tripled in the last five months, despite the Government's promise in the May budget to scale back the facility.

Lawyers and advocates say a large number of the people being sent to the island are being transferred from Australian prisons, and awaiting deportation on character grounds.

The partial closure of the Christmas Island's facilities was intended to be part of a broader so-called consolidation of the detention network, designed to save the Government $554 million over five years.

But the Immigration Department's own monthly figures reveal that since that announcement, the number of detainees on the Island has continued to rise dramatically.

At the end of April, there were only 80 detainees on the island, but by September, that number had risen to 221.

At least another 12 people have been transferred there since the beginning of the month, although official figures have not been released.

Immigration lawyer Michaela Byers has seen the trend reflected among her clients.

"That's occurred form Villawood and Yongah Hill and I've also had a few from Wickham Point," she said.

"So Sydney, Perth and Darwin immigration detention centres, they've been moving people to Christmas Island."

She believes it is a deliberate strategy by the Immigration Department.

"This pattern seems to be a way to punish those that are seen to be a nuisance or troublemakers, and also another way to crush people's hopes that they're never going to get a visa to Australia so they may as well voluntarily return," she said.

But it is not just asylum seekers who are being moved to the island.

A growing number of people are being deported by Australia on character grounds.

Under recent changes to the Migration Act, any foreigners who serve a prison sentence greater than 12 months automatically have their visas revoked.

They are often moved straight from prison to detention centres, such as Villawood, Yongah Hill and Christmas Island.

Asylum seekers housed alongside criminals

One Christmas Island detainee, who cannot be named, said the criminals being deported, so-called 501s, are detained alongside asylum seekers without any separation.

"Sometimes tension builds up here and it's very hard because nobody knows what's going on," he told the ABC.

"Each time we go to case managers, we ask them what is going on, how long are we going to be here – they don't want to comment, all they say is you've been brought here for operational matters."

He said the detention centre is not always safe.

"Sometimes it's dangerous because these other guys, they are very tough guys, they've been in jail and they make some problems for us here, like they beat us or maybe they feel annoyed very quickly or something.

"Sometimes it brings tension and they use it against us."

Greens Senator Sarah Hanson-Young has also commented on the Government's departure from its plan.

"I don't believe that Christmas Island is going to be scaled back in any reasonable timeframe, and I think that what is actually going on is the Government is planning on ramping up Christmas Island as another place to send people," she said.

Like immigration lawyer Michaela Byers, she believes the Government targets particular detainees to be sent there.

"The Government clearly is starting to use Christmas Island as a dumping ground for individuals that they don't want to have to deal with here on the Australian mainland, or indeed for people who are seen to be advantageous to be away from layers and advocates."

Ms Hanson-Young is sceptical the Government is serious about budget savings in this area.

"Of course offshore processing is always expensive, whether it's on Christmas Island or elsewhere, is always expensive, much more expensive than doing the detention of individuals onshore," she said.

"But if the Government really wanted to save money, the big expense is on Nauru, the big expense is Nauru and Manus Island.

"That's where billions and billions of dollars is being wasted every year on a relatively small handful of people that the Government is now in a quagmire as to how to deal with them.

"They can't be resettled in the long term on Nauru, no one is being resettled in PNG, meanwhile the Australian taxpayer is spending thousands and thousands of dollars, millions of dollars a day keeping those two expensive camps open."