MILLIONS of migrants and refugees are being denied adequate health care and should be included in the health systems of host countries as a human right, the World Health Organization said on Wednesday.

In its first attempt at reviewing the implications of migration on global healthcare policy, the WHO called for urgent action to support vulnerable populations who cross frontiers.

"Health does not begin or end at a country's border. Migratory status should therefore not be a discriminatory factor but a policy driver on which to build and strengthen healthcare," Santino Severoni, WHO's director of health and migration said in a statement.

Disease, famine, climate change and war are propelling the mass movement of people, with the conflict in Ukraine helping to push the total number of displaced people above 100 million for the first time ever. That is testing health systems in countries already battered by the COVID-19 pandemic.

"But the full extent of the impact of these upheavals is not yet understood because, as this report demonstrates, refugees and migrants are not fully visible in the available data – a serious gap that must be fixed," said Tedros Ghebreyesus, WHO director-general, in the report's foreword.

Refugees and migrants have health needs which may differ from those of host populations. Some have experienced high levels of food insecurity, for instance, and forced to skip meals or borrow money for food, the report found.

Overcrowded refugee camps have exacerbated the transmission of communicable diseases, such as tuberculosis, it said, adding that evidence suggested that the stress of adapting to a new environment, unemployment or trauma could increase substance abuse.

The report also highlighted how millions of migrant workers were employed in dangerous jobs, putting them at greater risk of work-related injuries and disease.