It's started

Hundreds of Haitian migrants and Dominicans of Haitian descent are crossing into Haiti each day from the Dominican Republic, fearing possible deportation, and Haiti's prime minister said the influx was causing a humanitarian crisis.

The surge in border crossings follows implementation last week of a new Dominican immigration law which requires undocumented individuals to register for residency under a "regularisation" programme.

Those unable to register and who do not have identity documents can be deported, Dominican officials have said.

While the Dominican government says there will be no mass deportations, undocumented migrants are taking no chances.

Haitian Prime Minister Evans Paul said Haiti, the poorest nation in the Americas, was struggling to cope with the influx.

"With the deportation of migrants from the Dominican Republic, we are in a climate of a humanitarian crisis," he wrote on his Twitter account on Thursday.

In the past week, around 12,000 Haitian migrants have streamed across the border into Haiti in packed buses and on foot, carrying bags of belongings on their heads and pushing wheelbarrows stacked with furniture and mattresses.

But changes to nationality laws and a 2013 constitutional court ruling have stripped children of Haitian migrants born in the Dominican Republic of their Dominican nationality, rights groups say.

This means they have no identity documents and are stateless.

"With a stateless population in the Dominican Republic estimated at more than 200,000 people, the consequences of expulsion could be devastating," Adrian Edwards, spokesman for the Office of the United Nations High Commissioner for Refugees, told reporters in Geneva earlier this month.