Only a handful of arrests appeared to take place, and they were reported in only a few cities. That was much different from the nationwide show of force that had originally been planned, in which Immigration and Customs Enforcement agents were expected to fan out in unison Sunday morning across immigrant communities in major cities. But authorities said more arrests would follow through the week.

The plans for the operation were changed at the last minute because of news reports that had tipped off immigrant communities about what to expect, according to several current and former Department of Homeland Security officials familiar with the matter. Instead of a large simultaneous sweep, the authorities created a secondary plan for a smaller and more diffuse scale of apprehensions to roll out over roughly a week. Individual ICE field offices were given the discretion to decide when to begin, one official said.

The first reports of ICE activity came in Friday and Saturday. In Chicago, a mother was a apprehended with her daughters, but the family was immediately released under supervision according to a person familiar with the operation.

In New York, ICE agents attempted two arrests Saturday in the Sunset Park area of Brooklyn, and a third in East Harlem, according to the New York Mayor’s Office of Immigration Affairs. “No arrests were made to our knowledge,” the office said in a statement.

An additional operation was reported in Florida.

Immigrant advocates in targeted regions of the country who were standing by to support anyone who was arrested were surprised to have a relatively uneventful day.

Sunday morning, about 30 volunteer “ICE chasers” had fanned out across the Atlanta suburbs, where many Latino immigrants live. But after nearly three hours without any reports of arrests, they returned to the offices of a local advocacy organization for coffee and doughnuts, saying they would start again Monday morning.

In Los Angeles, Shannon Camacho, a coordinator for the city’s rapid response network for immigrants, said the group’s work over the weekend, helping unauthorized families prepare for possible detentions, was not wasted. While there have been no mass arrests so far, she said, families are now better prepared for whatever happens in the future.

Camacho also warned against paying heed to speculation on the internet. “We do get a lot of false alarms on social media, and that causes a lot of panic in the community,” she said. “People are afraid to go outside, to go to church, to go to the grocery store, and that’s harmful.”

Immigration authorities planned to continue making arrests throughout the week in at least 10 cities. They had identified at least 2,000 targets for the raids, but may ultimately arrest fewer. Typically, only 20 to 30% of the targets of ICE enforcement are apprehended. And because agents cannot legally force their way in to the homes of their targets, they rely on the element of surprise to be successful — suggesting that the current, highly publicized raids could result in even fewer arrests than usual.

The operation is one of the first to target not just adults who are in the country illegally, but parents and children who are part of the recent wave of migrant families who have arrived from Central America and elsewhere on the southern border, many of them seeking asylum from violence in their home countries.

All those targeted have been issued orders of deportation, in many cases because they failed to appear in immigration court as directed. Migrant lawyers say that a large number of recent arrivals were not informed of their court dates and did not know where or when to appear.

The operation was originally scheduled for late June, but it was postponed after harsh opposition from Democratic lawmakers and immigrant advocates. Trump confirmed Friday that it would go ahead over the weekend.

“They’re going to take people out, and they’re going to bring them back to their countries,” the president said. “Or they’re going to take criminals out, put them in prison, or put them in prison in the countries they came from.”

Millions of people live in the United States without documentation and are periodically targeted for deportation. These raids in particular were planned because of Trump’s frustration over the record numbers of migrant families who have been arriving from Central America, beginning last fall and increasing in numbers nearly every month since then. June was the first month this year in which arrivals decreased. The 28% drop that month was probably caused by the rising summer heat and the Trump administration’s pressure on Mexico to hold back migrants seeking to travel through that country.

“This is about the rule of law,” Mark Morgan, the acting commissioner of Customs and Border Protection, told “Fox & Friends” on Sunday. “Those individuals who remain here illegally, especially those who’ve received due process more than any other nation in the world would provide someone that came here illegally, to include those with final orders, that there are consequences to those that remain here illegally.”

Despite the operation’s low-key rollout, the threat alone was enough to spark concern and upend weekend plans for many unauthorized immigrations, including those who feared that the raids could sweep up far more people than just those who were targeted.

Many were hunkering down indoors or went into hiding as far as possible from the addresses that the federal authorities had on file for them.

One family canceled a vacation to Florida on the advice of their lawyer, who had said that traveling could put the father, who is living in the country illegally, at risk.

Norelia Sanchez, an immigrant family support worker with the Redlands Christian Migrant Association in Immokalee, Florida, said local residents started calling her at 6 a.m. Friday, saying that ICE agents were “knocking door by door” in the town, a modest agricultural community of about 25,000 people about 40 miles east of Naples.

Some parents called the center’s offices that day to say they were too scared to send their children to summer day care and education programs. “The ones who did, you could actually see mothers with children, holding their hands, holding their cellphones, and they were literally running to the school,” Sanchez said.

During large-scale immigration raids, many people turn to social media to monitor the location of agents, trying to keep themselves safe.

Before the latest raids, immigrant advocates had attempted their own detective work, trying to ferret out where and how the arrests would be conducted. In Atlanta, lawyers began posting on social media based on a report that ICE agents had rented 40 minivans for the week, a rumor that quickly spread but remained unconfirmed.

Those arrested were expected to be held in detention centers in Texas and Pennsylvania that are specially equipped to hold families. But because of space limitations, some would probably be booked into hotel rooms until their travel documents could be prepared, ICE officials said. The agency’s goal is to deport the families as quickly as possible.

There were a large number of deportations during the Obama administration, but they mainly involved single adults who had been convicted of crimes.

“During Obama, the overwhelming majority of enforcement actions targeted criminal aliens,” said John Cohen, former acting undersecretary at the Department of Homeland Security during the Obama administration. “This operation apparently specifically targets families who for the most part present no risk.”

While ICE agents must wait for their targets to come outside of their homes voluntarily in order to arrest them, they are expected to come prepared with common tactics they have used in the past to coax their targets into cooperating. For example, agents often carry decoy photos, holding them up to the windows of migrants who are being targeted and pretending to be looking for someone else, to persuade them to open the door.

Agents also sometimes claim to be police officers responding to calls about domestic disturbances or gas leaks. They also have used social media to capture targets by making fake accounts on online dating websites and arranging rendezvous.

Cohen said the raids were impractical and not likely to improve the situation at the border — where holding facilities have been overrun recently, and as a result, migrants have been living in substandard conditions.

This article originally appeared in The New York Times.