Barack Obama removes threat of deportation for nearly 5 million people in sweeping immigration reforms

US president Barack Obama has imposed the most sweeping immigration reform in a generation, easing the threat of deportation for about 4.7 million undocumented immigrants and setting up a clash with Republicans.

Mr Obama's actions bypass the Congress in a country where immigration is an incredibly divisive issue.

With 11 million undocumented immigrants in the country, Mr Obama's plan would let 4.4 million people who are parents of US citizens and legal permanent residents remain in the US temporarily, without the threat of deportation.

Those undocumented residents could apply legally for jobs and join American society, but not vote or qualify for insurance under the president's signature healthcare law.

The measure would apply to those who have been in the US for at least five years.

An additional 270,000 people would be eligible for relief under the expansion of a 2012 move by Mr Obama to stop deporting people brought illegally to the US as children by their parents.

In the televised speech, Mr Obama addressed lawmakers angry about his executive immigration actions.

"To those members of Congress who question my authority to make our immigration system work better, or question the wisdom of me acting where Congress has failed, I have one answer: Pass a bill," Mr Obama said.

He said the real amnesty would be "leaving this broken system the way it is".

Trying to deport all 11 million people living in the country illegally was not realistic, he added.

Mr Obama also issued a warning to would-be border crossers that his actions, though they protected millions of undocumented immigrants, would not protect them.

"If you plan to enter the US illegally, your chances of getting caught and sent back just went up."

Republicans enraged by actions of 'Emperor Obama'

Republicans offered a strident reaction to Mr Obama's unilateral plan, many looking for ways they might neutralise the executive order.

"That's just not how our democracy works," House speaker John Boehner said in a statement.

"The president has said before that he's 'not king' and he's 'not an emperor', but he's sure acting like one."

Mr Boehner said Mr Obama's actions had sabotaged chances for bipartisan legislation.

"All year long I have warned the president that by... threatening action repeatedly on immigration, he was making it impossible to build the trust necessary to work together," he said.

"With this action, the president has chosen to deliberately sabotage any chance of... bipartisan reform that he claims to seek."

Homeland security committee chairman Michael McCaul branded the immigration plan "unconstitutional and a threat to our democracy".

But Mr Obama said his political opponents had enough time to pass laws that even Republican senators agreed to last year, and because they had not he would act alone.

"If you've been in America for more than five years, if you have children who are American citizens or legal residents, if you register, pass a criminal background check and you're willing to pay your fair share of taxes, you will be able to apply to stay in this country temporarily without fear of deportation," he said.

"You can come out of the shadows and get right with the law. That's what this deal is."

While most Democrats are thought to support the president, he received criticism from his own ranks.

Senator Joe Manchin opposed Mr Obama's unilateral step, but said he also disagreed with the House's decision not to vote on the bipartisan reform bill that passed the Senate in June 2013.

"Congress must work with the president to debate the issues and vote to secure our borders, create a tough legalisation process, and ensure employers don't hire illegal immigrants," Senator Manchin said.

High-profile Democrat Hillary Clinton fired off a tweet after Mr Obama's speech, suggesting immigration would be a crunch debate topic in the next presidential campaign.

"Thanks to [Mr Obama] for taking action on immigration in the face of inaction. Now let's turn to permanent bipartisan reform," wrote Ms Clinton, the prospective frontrunner in the 2016 presidential race.

Mr Obama's plans are a big deal for America's Hispanic community with hundreds gathering outside the White House as the speech went to air, waving American flags.

The irony of American immigration is that in spite of millions living illegally, there is a system in place to sustain them.

They have the right to drivers' licences, their children can get primary education with no questions asked, and they can even pay tax and claim tax credits for children.

But some people have dubbed Mr Obama the deporter-in-chief, deporting 2 million people during his time in office - 400,000 people in the past year alone.

Some of those lucky enough to be given a chance for a new legal status are just a few blocks away from Washington's Capitol Hill.

Many are young people who never realised they or their parents were illegal until they began applying for college.

"There are millions of families out there who are paying taxes, contributing to our community, who are volunteering, who have children who are going to school, children who are graduating with exceptional grades but then can't go to school or can't get that full ride because they don't have that status," Griselda Macias from the Latin American Youth Centre said.

Ms Macias, whose father was an illegal immigrant granted amnesty by president Ronald Reagan, hopes her students will no longer live in fear that a simple traffic stop by a police officer will get them deported.

"I've broken down several times and they [students] are stronger than I am at times, but I've broken down in front of them and cried because I feel so frustrated for the situation, for the fact that they're so resilient and say 'well I will make it work'. It is amazing."

• ABC/wires*