DENVER – Fear and anxiety spread through immigrant communities nationwide over anticipated federal raids aimed at detaining and deporting thousands of people accused of remaining illegally within the United States.

Immigration reform advocates said that communities around Atlanta, Baltimore, Chicago, Denver, Houston, Los Angeles, Miami, New York and San Francisco were being targeted by raids expected to start Sunday and last through at least Thursday.

“It’s almost like getting ready for a hurricane – it’s that state of alarm that people are feeling,” said Melissa Taveras of the Miami-based Florida Immigrant Coalition. “People are asking, ‘Is it OK for us to go work? Is it OK to take our kids to school?’”

The raids are different from routine Immigration and Customs Enforcement detentions, and advocates for immigrant communities say the raids appear designed to sow terror and discord among the approximately 2,000 families expected to be targeted, especially in light of news reports of some detainees dying in custody.

“It terrorizes the community,” said Milli Atkinson, legal director of the San Francisco Immigrant Legal Defense collaborative in San Francisco. “It’s really going to impact our community to see that happen, because with any detention they’re separating the men and the women and the children.”

The Trump administration argues the nation's immigration laws have long been ignored, and that tougher enforcement is necessary because Congress has failed to pass comprehensive immigration reform. The president on Friday said the raids would primarily target immigrants who have already been convicted of other crimes.

In Denver, Mayor Michael Hancock said city police officers would avoid helping ICE agents but said city human service workers were on alert to assist any minor children left behind if their parents are arrested.

In many cases, immigrants who lack legal permission to remain in the United States have minor children who are U.S. citizens. That puts officials in liberal cities like Denver or San Francisco in the tough position of opposing the ICE raids themselves but still having to manage the consequences.

"We're not going to put children in cages or leave them in inhumane conditions," Hancock said during a call with reporters on Friday morning. "Our job is to help those families as best we can."

Immigrant advocates say many of the people expected to be targeted in the raids have been issued a "final order of removal" but were never told when or where that previous hearing was taking place, and thus never attended.

In Houston, a city of 1.6 million immigrants and more than 500,000 undocumented immigrants, the phone at FIEL Houston, an immigrants’ rights group, has been ringing non-stop and five forums the group organized since the raids’ announcement have been standing-room only, said Cesar Espinosa, FIEL’s executive director.

“There’s a lot of tension in the community right now,” he said.

FIEL created a “rapid-response network,” enlisting around 80 community members throughout the city who will alert the group if and when a raid is happening. The goal is to get to the scene of the raid as it’s happening, document the procedure and advise the targeted immigrants of their rights, Espinosa said. One of their biggest concerns is that undocumented immigrants who are not the target of the raids get swept up in the operations, he said.

“We hope nothing happens,” Espinosa said. “But if something does happen, we’re preparing our community to be ready to react.”

Elsewhere, advocates were preparing fliers and staffing hotlines to alert immigrant communities of their rights, including requiring a judicial warrant to enter a private home. Advocates said ICE agents working routine removal cases usually stake out their targets' homes and wait for them to leave for work, and that Sunday operations would be highly unusual.

“Sometimes with this administration, there’s so many attacks that [undocumented migrants] feel like there’s no recourse," said Shannon Camacho of the Coalition for Humane Immigrant Rights of Los Angeles. "Don’t open your door. Remain silent. They don’t have to offer any information to ICE, and ICE can’t enter their homes unless they have a judicial warrant, signed by a judge. The vast majority of the time, they don’t have those warrants."

In New York City, the New Sanctuary Coalition’s New York branch and the New York Immigration Coalition planned a rally for Friday night, against both the southern border detention camps and the expected ICE raids.

“While maybe the scale of what ICE will be doing this weekend will be more than what they actually do at any one time … the reality is that immigrant communities have been living under this kind of fear for the last two-and-a-half years,” said Anu Joshi, senior director of immigrant rights policy for the New York Immigration Coalition.

The coalition, representing more than 200 member organizations across New York State, has joined with local organizations in know-your-rights training classes for immigrant communities and other instructional services.

“It’s not just during the raids that people need to know their rights,” said Joshi. “For the last two-and-a-half years ICE has been indiscriminately going in and targeting people.”

Bitta Mostofi, commissioner of the New York City Mayor’s Office of Immigrant Affairs, condemned the anticipated raids during a Friday morning interview with NY1, the city’s 24-hour cable news channel.

“You have to call it what it is, and say clearly that this is deplorable and cruel,” said Mostofi. “You are talking about instilling fear and chilling people who in some cases have been here for decades, and others who have U.S. citizen families and children. It is a moment in time for us, certainly as a city and community members, to ensure we are empowering our communities, making sure you know you have rights regardless of your immigration status, and that you can access free and safe legal support that the city has funded.”

Manhattan District Attorney Cyrus Vance Jr. added his voice in opposition to the raids. "NYC is living proof that sanctuary policies make us safer," he tweeted.

In Atlanta, Mayor Keisha Lance Bottoms called the looming raids Friday "unwelcome."

"The White House is compounding an already spiraling humanitarian crisis with detention centers,” Bottoms said in a statement. “If they want to truly help cities, they should ask us what we need, because political shows of force will only harm—not help.”

Many large U.S. cities, including Los Angeles, Denver, Seattle and Miami, have declared themselves "sanctuaries" for undocumented immigrants, and adopted policies barring local government workers from cooperating with federal immigration authorities. Federal raids risk severing the carefully built bonds between local police and immigrant communities, Hancock said, making it less likely that undocumented immigrants would ask for help or testify in court against violent criminals.

On Friday, San Francisco Mayor London Breed reiterated that the city’s police would not cooperate with any ICE operations and that the city was gearing up to protect its immigrants. “If you want to come after them, you’re going to have to come through us,” she said.

It remained unclear how the Trump administration would process and house the large number of detainees, with some advocates saying they had heard people might be kept in hotels if there wasn't enough space in already overcrowded detention centers.

Officials from Marriott International and Choice Hotels said they did not want their facilities used for such purposes.

“While we have no particular insights into whether the U.S. government is considering the use of hotels to aid in the situation at the border, Marriott has made the decision to decline any requests to use our hotels as detention facilities,’’ the company said in a statement.

Sara Nelson, president of the Association of Flight Attendants-CWA, called on airlines to say they won’t work with ICE during the raids.

“We need your commitment and moral clarity,’’ Nelson said in a tweet Friday singling out United, American, Delta, Alaska, Spirit and Frontier.

Flight attendants were highly critical of reports last summer that airlines were transporting children separated from their families, and several airlines pledged not to carry them. Last month, the union’s board unanimously passed a resolution “to support keeping families together, children safe and in opposition to ICE raids that are spreading fear in our communities.’’

Nelson also praised Marriott International’s decision not to house detainees at its hotels.

Contributing: Rick Jervis in Houston, Elizabeth Weise in San Francisco, Kevin McCoy in New York City, Jared Weber in Los Angeles, Nicquel Terry Ellis in Atlanta, Dawn Gilbertson in Chicago and Alan Gomez in Miami.