Gay asylum seekers on Manus island are being told they will be reported to the PNG police if they engage in homosexual relations while in detention, a new report by Amnesty International says.

The report is the second damning assessment of the government's offshore detention regime in less than a month, and identifies “a host” of human rights violations in Australia’s regional processing centre in Papua New Guinea.

It raises serious concerns about the treatment of gay asylum seekers who have been told by the most senior Australian immigration official on the island, Renate Croker, that if any sexual relations occur they would automatically be reported to the local police, the report claims.

“It is not clear what her statements are based on, as the [PNG] Criminal Code does not require mandatory reporting,” the report says.

Homosexuality is illegal in PNG.

One asylum seeker, “Alex” told Amnesty, “We have no support for our emotional problems. I’d like to have a boyfriend, to talk about the future with, to share my feelings with, but I’m too scared. All I want is a couple of hours to be together without attracting attention.”

Alex told Amnesty that some gay men have been bullied by staff and detainees and a number of gay men had returned to their country of origin as a result.

Amnesty’s report follows a five-day visit by officials to the offshore centre last month, and raises substantial concerns over the facilities and treatment of asylum seekers on Manus. In particular it raises cases which show that a number of unaccompanied minors may have been transferred to the centre in error; that disabled asylum seekers are not being afforded proper medical treatment; that poor conditions in certain parts of the camp constitute harsh and deliberate cruelty violating the UN convention against torture, that asylum seekers are being verbally abused by staff and that the slow processing of refugee claims is designed to encourage asylum seekers to return to their country of origin.

In November, the UN’s refugee agency published an inspection report also documenting a number of international human rights law violations on Manus.

Researchers for the Amnesty report, entitled “This is breaking people”, interviewed three asylum seekers on Manus who said they were between the ages of 15 and 17. The three were being detained with adults in direct contravention of international law, the report says. Amnesty say that Australian immigration officials were alerted to the cases but had been determined the asylum seekers were over 18.

“The treatment of their cases raises serious concerns about the age determination procedures employed by Australia’s Department of Immigration and Border Protection (DIBP) which appear to weigh discrepancies in children’s accounts heavily against them, treated proffered identity documents as presumptively fraudulent, rely heavily on observations of physical appearance, and in general not to give children the benefit of the doubt in close cases, as required by international standard.”

In early November Guardian Australia revealed that two unaccompanied minors were being held in isolation on Manus in a small compound, as a result of administrative error. Both teenage boys have been returned to Christmas Island.

Immigration minister Scott Morrison has repeatedly said that the government has no policy of transferring children to Manus.

The report also gives details of conditions inside a number of sectors of the regional processing centre, raising particular concern over one section, “P dorm” in Foxtrot camp.

The dormitory houses 112 men in “overcrowded conditions” who share “two small working fans” between them.

“The mixture of stifling heat, sweat and moisture leaves a permanent, overwhelming stench. Asylum seekers reported finding snakes in the room and flooding when it rained,” said Graeme McGregor, Amnesty’s Refugee Campaign Coordinator.

The report also includes accounts of a lack of access to drinking water in certain areas of the centre.

Some asylum seekers interviewed by Amnesty give accounts of verbal abuse by staff. The report says that asylum seekers are routinely referred to by their boat identification numbers rather than by name. Others reported more direct verbal aggression, the most frequent the report says, “was being told to return to their country of origin, “go home” or “go back to your country”, particularly as a response by staff to requests for items or improvements in conditions”.

The report also echoes criticisms voiced by the UNHCR that processing of refugee claims on Manus was so slow that it had been designed to encourage people to return to their country of origin, irrespective of their refugee claims.

The report recommends an end to offshore processing in PNG.

The minister for immigration and border protection, Scott Morrison, dismissed the recommendation of halting offshore processing but said in statement: “Where practical, suggestions raised to improve the operations of our offshore processing centres will be given proper consideration.”

He added: “The government, in partnership with our partners in Nauru and PNG, have already acted to reactivate processing of claims on Nauru and Manus and to rapidly expand the capacity and nature of facilities at both Nauru and Manus, to address the deficiencies we identified when coming to Government, some of which are also noted in the Amnesty Report."

He did not respond to specific questions posed by Guardian Australia about the treatment of gay asylum seekers on Manus.