LOS ANGELES, United States (AFP) — A coalition of Democratic-leaning states launched legal actions Tuesday seeking to block Donald Trump's plan to end birthright citizenship in the United States.

The two separate lawsuits involving a total of 22 states, including California and New York, come the day after Trump took office and quickly unveiled a phalanx of executive orders he hopes will reshape American immigration.

Chief among them was an order eliminating the automatic granting of citizenship to anyone born on US soil, a right guaranteed by the 14th Amendment of the country's constitution.

If implemented, the order would prevent the federal government from issuing passports, citizenship certificates or other documents to children whose mothers are in the country illegally or temporarily, and whose father is not a US citizen or permanent resident.

"The President's executive order attempting to rescind birthright citizenship is blatantly unconstitutional and quite frankly, un-American," California Attorney General Rob Bonta said as he announced the suit.

"We are asking a court to immediately block this order from taking effect and ensure that the rights of American-born children impacted by this order remain in effect while litigation proceeds."

"The President has overstepped his authority by a mile with this order, and we will hold him accountable."

The California-led suit, which was filed in federal court in Massachusetts, was joined later Tuesday by one filed in Washington state, and comes alongside a similar suit filed by the American Civil Liberties Union and other advocacy groups in New Hampshire.

The 14th Amendment was adopted in the aftermath of the US Civil War, as part of an effort to ensure the rights of former slaves and their children.

It says, in part: "All persons born or naturalized in the United States, and subject to the jurisdiction thereof, are citizens of the United States and of the State wherein they reside."

Trump's order, if it stands, will come into effect 30 days from when he signed it.

The president acknowledged as he put pen to paper that it was likely to face legal challenges.

"I think we have good grounds, but you could be right. I mean, we'll find out," he said, when asked about the likelihood of a legal effort to halt it.