After not even 18 months in office, Mayor Eric Adams of New York City has lost one top official after another from his administration, a troubling and unusual exodus as the city is confronted by multiple major challenges.

Last month, the mayor’s chief housing officer, Jessica Katz, announced her resignation, leaving the city without the architect of its housing agenda. In February, the city’s social services commissioner, Gary Jenkins, resigned. And on Monday, the city’s police commissioner, Keechant Sewell, blindsided Mr. Adams with her resignation.

Their departures have hit the Adams administration in areas where the city faces its most pressing concerns: crime, housing and homelessness.

They are hardly alone. Mr. Adams has already lost his first deputy mayor, his chief of staff and his buildings commissioner. And by the end of the summer, Mr. Adams’s chief counsel, communications director and chief efficiency officer also plan to step down.

While their reasons for leaving vary, police and City Hall officials close to Ms. Sewell said she was undermined by Philip Banks, the deputy mayor for public safety, who some felt was acting as a shadow police commissioner.

“It’s been clear for a while that Commissioner Sewell was being boxed in,” said Diana Ayala, the deputy speaker of the City Council. “You have a woman in leadership and you are not allowing her to lead. She stopped going to press conferences a long time ago. She’s perfectly qualified to do her job. Let her do her job.”

The overwhelming number of resignations — typically not seen until far later in a mayor’s first term — reinforces the notion that Mr. Adams trusts few people beyond a tight circle of loyalists who serve as deputy mayors and senior advisers.

The loss of experienced government hands threatens to enhance that dynamic, further empowering the mayor’s longtime loyalists at a time when the city is facing a phalanx of challenges: a housing crisis, a potentially looming commercial real estate crash, intensifying federal scrutiny of its jails, record levels of homelessness, an influx of asylum seekers from the southern border, and the arrival of summer, which typically comes with higher rates of violence.

Mr. Adams on Tuesday angrily rebuffed the notion that he was facing a staff exodus, and accused the media that covers him of existing in a narrative-generating “bubble.” He noted that he oversaw more than 300,000 employees, and the high-level departures represent just a fraction of the city work force.

“And we’re saying, is everybody running for the door?” he said. “No, everybody is running to do their job.”

Reached by phone on Tuesday afternoon, Ms. Sewell declined to comment on her exit.

Deputy Mayor Banks said in a text that any suggestion of meddling was “untruthful gossip” and to call him for comment “when you get a quote from Commissioner Sewell.”

Max Young, the mayor’s communications director, who will step down this summer, attributed the spate of departures to the unusually stressful nature of government work these days.

“This is an unprecedented moment in New York’s history and we should acknowledge that everyone who works in public service is under tremendous pressure to manage myriad crises,” Mr. Young said. “People will leave, but one thing remains the same: our commitment to handling the crises we inherited, turning this city around, and improving the lives of all New Yorkers.”

The departures are not completely without precedent. In 1979, a year and a half into his first term as mayor, Ed Koch decided the structure of his administration was unwieldy, and eliminated four deputy mayor positions.

But that analogy only goes so far.

“That was sudden and abrupt,” recalled George Arzt, then the City Hall bureau chief for The New York Post, who joined the Koch administration in its third term. “This is just a slow drip, as one high-ranking official goes after another.”

Mr. Adams has long prized loyalty. He kept allies close as he rose through New York City politics to the top job. Ingrid Lewis-Martin, perhaps his closest aide, worked for Mr. Adams when he was a state senator and Brooklyn borough president, and is known to be fiercely protective. His transportation commissioner, Ydanis Rodriguez, is a political ally who campaigned for Mr. Adams and attacked one of his rivals.

His education department is run by David Banks, Philip Banks’s brother. His new first deputy mayor is Sheena Wright, David Banks’s fiancée.

The hiring of the mayor’s brother, Bernard Adams, to oversee his security also raised alarm among government watchdogs. His brother eventually took the position at a salary of $1 and stepped down in February. Bernard Adams’s wife, Sharon Adams, was hired the next month as a “strategic initiative specialist” at the Education Department with a $150,000 salary, the news outlet The City reported this month.

Outsiders have sometimes faced a more difficult road.

Ms. Katz, the city’s chief housing officer, had spent a decade in city government and was widely respected for her work in housing advocacy, but she was not an Adams loyalist. She decided to step down aftergrowing frustrated with the mayor’s opposition to City Council legislation that would have made it easier for people to leave homeless shelters for more stable housing.

At least two top officials left the Adams administration after being investigated. Gary Jenkins, the social services commissioner, was investigated over his response to homeless families applying for shelter; that investigation is believed to be ongoing. Eric Ulrich, the buildings commissioner, resigned in November after he was questioned by prosecutors from the Manhattan district attorney’s office who are investigating him for possible organized crime ties and illegal gambling.

Mr. Jenkins said on Tuesday that high-profile jobs in city government were stressful and that each official had to decide what was best for them. Mr. Jenkins is now a managing director at a consulting firm run by another Adams administration alumni: Frank Carone, the mayor’s former chief of staff who left in December.

“Every administration has its ebbs and flows,” he said. “One year is a dog year in an administration. I served in government for 36 years — I wanted to move on and try something else new.”

In the case of Ms. Sewell, she was an outsider spearheading a department central to Mr. Adams’s agenda — bringing down crime in a post-pandemic New York City.

As a former police captain, Mr. Adams ran on the notion that only he had the requisite experience to tamp down disorder. And on that front he has had some success, with this year seeing double-digit drops in shootings and murders.

Bill de Blasio, Mr. Adams’s predecessor, compared Mr. Adams’s intense focus on crime to his own emphasis on universal prekindergarten, an area in which he had experience as a former public school parent and school board member. In that context, Mr. de Blasio said, Mr. Adams’s close oversight of the Police Department made good sense.

“He obviously has real expertise as a former officer,” Mr. de Blasio said. “He ran on the issue. It was the issue he owned in the campaign and ever since. And crime is down. The result is what matters.”

Despite the widespread expectation that Ms. Sewell would not last long in a role that seemed untenable, Mr. Adams was surprised at the timing of Ms. Sewell’s departure.

At a news conference on Monday about safe streets, Mr. Adams praised Ms. Sewell and gave no indication that her resignation was imminent. Hours later, Ms. Sewell walked into City Hall, a meeting that was closely followed by an email she sent announcing her resignation. She made no mention of Mr. Adams.

The fact that Ms. Sewell’s resignation letter leaked before City Hall could announce it was striking. Under Mr. de Blasio, even with tense departures, announcements were generally coordinated and officials kept up the facade that the decision was mutual, and the situation cordial.

Mr. Adams on Tuesday acknowledged that he could be something of a heavy-handed manager. He recalled how his mother used to tell him, “If you don’t inspect what you expect, it’s all suspect.”

“Now some people may call that a micromanager,” he said. “I call it being the mayor of a city that you love.”