LONDON (AFP) - Asian cities are among the most equal in terms of income, but inequalities are widening as the income gap between rural and urban areas grows, the UN population programme said in a report Wednesday. Beijing is the most equal city in the world, while Jakarta and Phnom Penh also score highly, UN-Habitat said in its annual report on the state of the world's cities. Hong Kong is the most inequal city in Asia, while South African cities led by Johannesburg are the most inequal in the world. However, many Asian countries are grappling with expanding income disparities between rural and urban areas, which is fuelling migration to cities and threatening social harmony, the report said. The United Nations says inequalities in income and in access to adequate shelter can lead to a reduction in economic efficiency and spark social unrest. UN-Habitat head Anna Tibaijuka told a news conference in London that she was concerned the global financial crisis would aggravate the inequalities and could even lead to rioting as people struggled to pay the rent. "You cannot have a harmonious society if people are not secure in their homes," she said. "And if you cannot pay the rent, you are not secure in your home." The study also found that more than a third of urban dwellers in Asia live in slums. It said concentrations of slums throughout Asia varied widely, with the highest concentration in southern Asia. Asian cities are also among the most vulnerable in the world to their surrounding environment. Eighteen out of 20 of the largest cities in the region are located on the coast or on a river bank or delta, putting them at risk from rising water levels, the report said.