Last year in New Jersey, federal immigration officers took more than 1,300 undocumented migrants into custody. That figure was roughly 300 more than in 2023.

But on Thursday, less than a week into President Trump’s second term, the arrests of three people at a fish distribution warehouse in Newark appeared to tap a well of pent-up fear about mass deportations in a region teeming with immigrants.

The streets around the warehouse filled early Friday with television crews. Newark’s mayor held a news conference to decry the methods used by Immigration and Customs Enforcement officials as unconstitutional and blamed Mr. Trump, who campaigned on a promise to initiate the “largest deportation program in American history.”

Whether Thursday’s arrests in Newark’s Ironbound neighborhood were part of a new crackdown, or fairly typical of ICE enforcement actions in the city in recent years, was not immediately clear. Immigration arrests in the city are common. Last month, under former President Joseph R. Biden Jr., ICE officers based in Newark announced 33 arrests to little public notice. And ICE officials did not reply to several requests for comment.

But the enforcement activity left immigrants across the region on edge. There were reports of ICE officers knocking on doors in Vineland, in New Jersey’s southern agricultural region, which is heavily dependent on migrant labor. On Long Island, immigrant rights activists said they were busy fielding reports of “ramped-up” activity by ICE officers. And a police captain in Ossining, N.Y., Brendan Donohue, warned that rumors often multiply more quickly than facts.

“Fear spreads very quickly, and even just the suggestion that ICE could come here turns into a ‘ICE was here’ kind of a situation,” Captain Donohue said. “These things can snowball, of course.”