The United Nations refugee chief hailed Wednesday an agreement reached by EU countries and lawmakers to overhaul the bloc's laws on handling asylum seekers and migrants as "a very positive step".

"Congrats to the EU and @EU_Commission for reaching a political agreement," Filippo Grandi said on X, formerly Twitter.

"It is a very positive step. Now to its implementation! UNHCR stands ready to advise and support," added the UN's High Commissioner for Refugees, saluting the "perseverance and leadership" of European Commissioner for Home Affairs Ylva Johansson in thrashing out the deal.

An International Organization for Migration spokesperson also offered backing.

The "IOM welcomes the political agreement reached on the New Migration and Asylum Pact, which heralds a common, comprehensive and predictable EU framework and looks forward to its formal adoption," the spokesperson said.

"We appreciate that it recognizes the importance of states working together to make safe and regular migration work for everyone.

"Implementation will be key, and IOM is ready to support EU Member States with rights-based and humane application."

The EU has lauded the deal as a historic overhaul of its asylum system, with more border detention centres and speedier deportations.

However, migrant charities have criticised the changes as "dangerous".

The agreement still has to be formally adopted by the European Council and European Parliament.

EU member state Hungary has notably rejected a compulsory solidarity mechanism which is to be set up, providing for a certain number of migrant relocations spread between other EU countries.

Countries refusing to take in migrants would provide a financial or material contribution to those that do - something Budapest fiercely opposes.