NEW YORK -- President Donald Trump's immigration order sowed more chaos and outrage across the country Sunday, with travellers getting detained at airports, panicked families searching for relatives and protesters marching against the sweeping measure that was blocked by several federal courts.

Attorneys struggled to determine how many people had been affected so far by the rules, which Trump said Saturday were "working out very nicely."

But critics described widespread confusion and said an untold number of travellers were being held in legal limbo because of ill-defined procedures. Others were released. Lawyers manned tables at New York's Kennedy Airport to help families whose loved ones had been detained, and some 150 Chicago-area lawyers showed up at O'Hare Airport after getting an email seeking legal assistance for travellers.

"We just simply don't know how many people there are and where they are," said Lee Gelernt, deputy director of the American Civil Liberties Union's Immigrants' Rights Project.

Advocates for travellers say the chaos is likely to continue. The executive director of the National Immigration Law Center, Marielena Hincapie, said "this is just the beginning."

"We're really in a crisis mode, a constitutional crisis mode in our country, and we're going to need everyone," she said. "This is definitely one of those all-hands-on-deck moments."

On Sunday talk shows, White House officials defended Trump's actions.

"I can't imagine too many people out there watching this right now think it's unreasonable to ask a few more questions from someone travelling in and out of Libya and Yemen before being let loose in the United States," White House chief of staff Reince Priebus said.

White House adviser Kellyanne Conway described the changes as "a small price to pay" to keep the nation safe.

By Sunday evening, officials said nearly all of those who had been detained were free or soon would be, but the status of some travellers was unclear. The released included nine people held at Dallas-Fort Worth International Airport, Dallas Mayor Mike Rawlings' office said.

The people affected included a woman who was sent back to Saudi Arabia after travelling to Indiana to care for her cancer-stricken mother; a family physician who has lived in the U.S. for two decades who was held for nine hours; and a Minneapolis woman about to become a U.S. citizen who was questioned for 12 hours.

Meanwhile, protests continued across the country Sunday, from smaller airports like Rapid City Regional Airport in South Dakota to one of the nation's busiest, Hartfield-Jackson Atlanta International Airport.

Demonstrations first erupted Saturday, a day after Trump signed the order banning travel to the U.S. by citizens of Iraq, Syria, Iran, Sudan, Libya, Somalia or Yemen. The president also suspended the U.S. refugee program for four months.

In Washington D.C., hundreds of demonstrators gathered outside the White House, some holding signs that read, "We are all immigrants in America." Demonstrations also unfolded at Detroit Metropolitan Airport and Minneapolis-St. Paul International Airport, as well as in suburban Chicago, where a Jewish group organized a protest to support Muslims.

Lawyers in Chicago crowded into a food court Saturday at O'Hare, some walking around with signs offering legal help. One volunteer attorney, Julia Schlozman, was among those who jumped on a subway and headed to O'Hare.

"I just felt like I had to do something," she told the Chicago Tribune.

A federal judge in New York issued an order Saturday temporarily blocking the government from deporting people with valid visas who arrived after Trump's travel ban took effect. But confusion remained about who could stay and who will be kept out. Federal courts in Virginia, Massachusetts and Washington state took similar action.

A more decisive ruling on the legality of the Trump action by U.S. District Judge Ann M. Donnelly will probably take at least several weeks. Opponents and government attorneys will get a chance to lay out their arguments in filings and possibly in oral arguments in court, Gelernt said. Activists said their goal was to have Trump's order overturned entirely.

Chicago Cardinal Blase Cupich, known for usually tempering his public comments, did not hold back in a statement Sunday about Trump's measures: "Their design and implementation have been rushed, chaotic, cruel and oblivious to the realities" of security. They had, he added, ushered in "a dark moment in U.S. history."

The president of the University of Notre Dame, Father John I. Jenkins, was also among the ban's sharp critics.

"If it stands, it will over time diminish the scope and strength of the educational and research efforts of American universities," he said Sunday in a statement. And he added: "We respectfully urge the president to rescind this order."

An official with the Department of Homeland Security who briefed reporters by phone on Saturday said 109 people who were in transit on airplanes had been denied entry and 173 had not been allowed to get on their planes overseas.

No green-card holders were turned away from entering the U.S. as of Saturday, the official said, though several spent hours in detention before being allowed in.

After an appeal from civil liberties lawyers, Judge Donnelly issued an emergency order Saturday barring the U.S. from summarily deporting people who arrived with valid visas or an approved refugee application, saying it would likely violate their legal rights.

Before Trump signed the order, more than 67,000 refugees had been approved by the federal government to enter the U.S., said Jen Smyers, refugee policy director for Church World Service. More than 6,400 had already been booked on flights, including 15 families that had been expected over the next few weeks in the Chicago area from Ethiopia, Eritrea, Iran, Syria and Uganda.

The bulk of refugees entering the U.S. are settled by religious groups. All that work ground to a halt after Trump signed the order.

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Tarm reported from Chicago. Associated Press writers Verena Dobnik and Karen Matthews in New York, Olga Rodriguez in San Francisco and Caryn Rousseau in Chicago contributed to this report.