US President Joe Biden announced a sweeping plan on Tuesday to offer permanent residency status to hundreds of thousands of undocumented migrants who are married to US citizens.

The scheme will be open to around 500,000 spouses who have lived in the US for at least 10 years, as well as 50,000 children and young adults under the age of 21 who have a US-citizen parent.

"These actions will promote family unity and strengthen our economy," the White House said in a statement.

It contrasts sharply with Republican presidential nominee Donald Trump's plan for mass deportations.

How will the scheme work?

Previously, undocumented spouses would have to leave the US in order to apply for residency, separating them from their families.

Under Biden's new plan, those migrants who are approved will be granted work authorization and the right to stay in the US for up to three years while they apply for a green card.

Receiving a green card would also open up a pathway to becoming a US citizen.

Migration policy in the spotlight

The new policy received praise from migrant advocate groups but was criticized by some conservatives.

"The overwhelming majority of Americans support these humane and common-sense steps, and it will directly improve the lives of more than 10 million American citizens who have an undocumented family member," said Rebecca Shi, executive director of the American Business Immigration Coalition.

"Today, those families, and the advocates fighting on their behalf, can breathe a huge sigh of relief."

Meanwhile, Republican lawmakers panned the move.

"With the stroke of a pen, President Biden is now shielding 550,000 illegal aliens from deportation," said Congressman Josh Brecheen of Oklahoma.

"This is all in an effort to appease their family members hoping to garnish their votes for the upcoming election."

Biden's announcement comes on the 12-year anniversary of the Deferred Action for Childhood Arrivals program (DACA) that was introduced by then-president Barack Obama.

It also comes in the lead-up to the presidential election in November where Biden is expected to again face off against his 2020 election rival Trump.

zc/ab (AP, Reuters, AFP)