Bulgaria will not join a United Nations accord on regulating the treatment of migrants worldwide and would not attend the conference marking its formal adoption in Morocco next week, its centre-right government decided on Wednesday.

The Black Sea state's government said it would also abstain in a subsequent vote on a resolution in the UN General Assembly to endorse the already adopted pact in a move that highlights how Europe has turned colder on accepting foreigners.

At least five other EU countries, including Hungary, the Czech Republic, Poland and Slovakia, have already shunned the accord - a sign of how the bloc has turned increasingly restrictive on accepting refugees and migrants alike since a 2015 spike in arrivals.

"At this stage, the Bulgarian government believes that the decision not to join the Global Compact for Safe, Orderly and Regular Migration, protects to the fullest extent the interests of the country and its citizens," it said.

The pact, which addresses issues such as how to protect people who migrate, how to integrate them into new countries and how to return them to their home countries, was approved in July by all 193 member nations except the United States, which backed out last year.

It followed the biggest influx of migrants into Europe since World War Two, many fleeing conflicts in the Middle East and beyond.

The issue has led to a government crisis in Belgium, Austria has said it will not sign up and opposition from Italy's prominent interior minister, the right-wing Matteo Salvini, has thrown Rome's support into doubt.

In the Netherlands, a recent opinion poll showed 41% of people against signing the pact versus 34% in favour. Outside of the EU, Australia has also quit.

Bulgaria, a Balkan country with a population of 7 million, lies on one of the main migratory routes from the Middle East to western Europe, says it is already taking steps to stop illegal migration and protect the EU's external borders.