The Trump administration will now require people seeking green cards to leave the United States during the application process — a sweeping change that could upend the lives of hundreds of thousands of people seeking the right to legally and permanently live and work in the US.

The US has announced a new policy that makes it more difficult for immigrants who are already in the country to obtain a green card, or permanent residency.

"An alien who is in the U.S. temporarily ​and wants a Green Card must return to their home country ​to apply," said the U.S. Department of Homeland Security, which has oversight of USCIS.