Representatives from around the globe are gearing up for a major conference in Morocco to endorse a United Nations migration pact, despite a string of countries shunning the accord.

The Global Compact for Safe, Orderly and Regular Migration was finalised at the UN in July following 18 months of negotiations and will be formally adopted at the two-day gathering in Marrakesh starting Monday.

The non-binding UN accord, which aims to promote a common approach to growing migrant flows, has become a target for populist politicians who denounce it as an affront to national sovereignty.

The United States quit negotiations last December, and was followed by Hungary seven months later.

Since then, Australia, Israel, Poland, Slovakia, the Czech Republic, Austria, Switzerland, Bulgaria, Latvia and the Dominican Republic have either publicly disavowed the pact or notified the United Nations they are not participating.

Rows over the accord have erupted in several European Union nations, threatening to tear apart Belgium's coalition government and pushing Slovakia's foreign minister to tender his resignation.

But key backers led by German Chancellor Angela Merkel will be in Morocco to endorse the pact and the UN remains upbeat that it can help the world better cope with the hot-button issue.

"I am very confident: a large number of states continue to keep their word, they reached agreement on July 13 in New York after very serious and very intense negotiations," UN special representative for migration Louise Arbour told AFP.

"The countries dropping out of the process today had after all obtained concessions during the negotiations, and I must admit that I find it a little surprising."