LEIGH SALES, PRESENTER: Tonight, 7.30 can reveal that the recent cycle of violence in Australia's offshore detention network continues with another two women coming forward to say they've been raped.

The pair of refugees now lives freely in Nauru after Australia refused to accept them.

7.30 has obtained a chilling recording made in the moments after one of the attacks.

These two women are just the latest victims of sexual assault on Nauru and their cases have prompted another former centre worker to risk prosecution in order to reveal what she witnessed on the island.

Hayden Cooper reports, and a warning: this story contains distressing material.

'NAJMA': Hello?

POLICE OFFICER: It's the police.

'NAJMA': Where?

POLICE OFFICER: Where are you? We are outside the RPC3.

'NAJMA': No, um ...

HAYDEN COOPER, REPORTER: It's the middle of the night and this 26-year-old Somali woman is lost and distraught.

POLICE OFFICER: Can you see the police car yet?

'NAJMA': I can't see. I'm inside, in the rock (cave).

POLICE OFFICER: Inside the rock?

'NAJMA': Yeah.

HAYDEN COOPER: She had just reported being raped by two Nauruan men. This is the moment that police came to find her.

'NAJMA': Please, this man is coming back.

HAYDEN COOPER: 'Najma', as we'll call her, feared that the police would not believe her, so she filmed with one phone while calling for help with the other.

'NAJMA': I listen shout, ambulance. Please help me.

HAYDEN COOPER: Her ordeal is not an isolated case. In detention and in the community, the rape and sexual assault of asylum seekers and refugees in Nauru is not uncommon.

DANIELLE SERRANO, FORMER NAURU SOCIAL WORKER: It's a very real threat, it's a very real fear. I think it's very serious.

DANIEL WEBB, HUMAN RIGHTS LAW CENTRE: It's becoming clear that Nauru, both inside the detention centre and outside of it, is not a safe place for women and not a safe place for children.

HAYDEN COOPER: This is where refugees are settled in Nauru outside detention, the Nibok and Ewa camps. 'Najma' lives here. She filmed the place for 7.30.

'NAJMA' (subtitle translation): This is where the Australian Government has brought us. This is where we are kept.

HAYDEN COOPER: Although deemed a refugee, she's been told she'll stay on Nauru unless another country will take her.

'NAJMA' (subtitle translation): I'm a Somali girl. I was brought here to be safe, but I have no safety.

HAYDEN COOPER: On August 21st at about 6 pm, 'Najma' was out walking when she says she was dragged into the bushes by two masked Nauruan men. She says they raped her, hit her in the head and left her in a cave.

It took four hours for Nauruan police to arrive.

POLICE OFFICER: We, you go back to Camp 5. You see the light there.

HAYDEN COOPER: She was taken to hospital and provided this statement to police detailing the brutal incident. She says she's heard nothing since.

'NAJMA' (subtitle translation): No-one is doing anything about it. That's the problem we have here.

HAYDEN COOPER: 7.30 understands it's not the only recent alleged sexual assault in the community. This is the medical file of another refugee who has reported being raped. It reveals she's in the early stages of pregnancy. The woman wants to come to Australia to have an abortion.

Inside the detention centres, there are similar stories.

WOMAN: He comes inside and the door, I think we lock when we are sleeping and someone come inside as we are sleeping and he switch off the light.

DANIEL WEBB: We act for several women who've suffered sexual assaults on Nauru who've been returned to Australia for medical treatment. These are women of different ages with different histories from different parts of the world, but what they have in common is they are all absolutely terrified of being sent back to Nauru.

HAYDEN COOPER: Figures prepared for 7.30 reveal the extent of the sexual violence on Nauru, both in detention and in the community. At least 23 men, women and children say they have been raped or sexually abused. Most of them are now in detention facilities in Australia, but some have been sent back to Nauru. Not all victims reported their abuse to authorities.

So is the island a safe place to settle refugees?

DANIELLE SERRANO: I don't believe so, no. No.

HAYDEN COOPER: Danielle Serrano is going public for the first time. A former case worker for Save the Children, she spent almost six months working on Nauru.

DANIELLE SERRANO: I did not feel like it was a safe environment to be out and about by myself and I certainly don't think it's a safe environment for vulnerable women and children.

HAYDEN COOPER: She reveals that the Immigration Department has its concerns about the safety of women on Nauru. It repeatedly warned staff not to travel around the island alone.

DANIELLE SERRANO: It tells me that Immigration are aware. That they're aware that the environment is not safe. That made me quite frustrated, to be thinking, "How come you care about my safety and our safety as staff and as women, yet this is on the island that you want to release women and children into?"

HAYDEN COOPER: Defying the Border Force Act and risking jail for speaking out, Danielle Serrano says she was aware of threats of rape directed at refugees while they were still in detention.

DANIELLE SERRANO: Some of the local guards had said to them that they were looking forward to them being released because of what they would like to do with them. So, yes, I am aware of instances where that fear was made known.

HAYDEN COOPER: In 'Najma's case, she has little faith in Nauruan police. It's no wonder. In the past three years, detention centre operators have referred 50 incidents to local police for investigation. Just two convictions have been secured. 7.30 put several questions to the Nauruan police superintendent about rape and sexual assault on the island, but we received a reply from the country's Australian PR agent. "Due to continued unbalanced and inaccurate coverage of Nauru by the ABC," he said, "we will not respond to this request."

Daniel Webb is a lawyer at Melbourne's Human Rights Law Centre.

DANIEL WEBB: As much as the Nauruan Government might try and say otherwise, the reality is that the Nauruan justice system and the rule of law in Nauru is in complete disarray. Not only is Nauru an unsafe place for vulnerable women and children that Australia sends there, but the Nauruan justice system can't protect them.

'Najma' is now stuck on Nauru with a five-year visa. Her future is uncertain.

'NAJMA' (subtitle translation): The Nauruan men have set up a checkpoint here. They charge us $5 to use the road. This is where we are assaulted. When we go to our cleaning jobs, the men come and harass us. ...

... (Sobbing) I listen your shout. Please come help me.

HAYDEN COOPER: Her harrowing recording is just the latest evidence of the trauma on Nauru, a place where journalists are effectively barred and those who've worked there risk jail in Australia by talking about what they saw.

DANIELLE SERRANO: Professionally and ethically, I can't know this and not say something. Every Australian needs to know that this is what our votes have gone for and this is what our taxpayer dollars allow. Are we OK with that?

'NAJMA': I listen your shout. Please, this man is come back.

You can read the Immigration Department response to that story.