A move to ban rough sleeping in Melbourne has been condemned by a senior United Nations official as violation of human rights law, in a shock development likely to prove highly embarrassing for the world's most liveable city.

The United Nations Special Rapporteur on the Right to Housing, Leilani Farha, said a plan to outlaw people camping in the city and fine those who leave their personal items unattended was a serious international human rights concern.

"The criminalisation of homelessness is deeply concerning and violates international human rights law," Ms Farha said via a statement from the Office of the United Nations High Commissioner for Human Rights in Geneva.

"The proposed law goes further and is discriminatory – stopping people from engaging in life-sustaining activities, and penalising them because they are poor and have no place to live."