The United States has announced a major immigration policy change that will require most people seeking green cards to apply from outside the country.

US Citizenship and Immigration Services said on Friday that immigrants applying for a change in status must now go through consular processing at US embassies or consulates abroad “except in extraordinary circumstances”.

The policy affects people already in the US on student, work or tourist visas who previously could apply for permanent residency without leaving the country.

USCIS said the move is intended to strengthen immigration enforcement and reduce visa overstays.

“When aliens apply from their home country, it reduces the need to find and remove those who decide to slip into the shadows and remain in the US illegally after being denied residency,” the agency said, adding the system would become “fairer and more efficient”.

USCIS spokesman Zach Kahler said: “From now on, an alien who is in the US temporarily and wants a green card must return to their home country to apply, except in extraordinary circumstances.”

Critics say the new rules could separate families and disrupt employers relying on immigrant workers.

Former USCIS official Michael Valverde told CBS the policy would “disrupt the plans of hundreds of thousands of families and employers annually”.

It remains unclear whether pending green card applications will be affected under the new system.