New York City hurtled into uncharted territory Thursday as prosecutors accused Mayor Eric Adams of a decadelong scheme of soliciting foreign campaign donations through straw donors in exchange for official favors.

Mr. Adams, a Democrat who vowed to return swagger to New York, denied the charges and pleaded for patience during an awkward press conference in the rain. He was met with heckles and calls to resign from political rivals and liberal groups who want public advocate Jumaane Williams to step in as acting mayor.

New York Gov. Kathy Hochul, a Democrat, could take the unprecedented step of suspending Mr. Adams and removing him after a 30-day period that allows him to offer a public defense. She said Thursday that the indictment was a serious matter and she would be “deliberative” and try to do the right thing for state residents.

Others simply hoped for the best.

“A jury of the mayor’s peers will now evaluate the charges in the indictment and ultimately render a determination. In the meantime, I pray for the well-being of our great city,” said House Minority Leader Hakeem Jeffries, New York Democrat.

The 57-page indictment unsealed Thursday alleges that Mr. Adams, who faces reelection next year, funneled foreign campaign donations through U.S. people who posed as the source of the money and then used his official power to provide favorable treatment for the “illicit benefits he received.”

“Mayor Adams took these contributions even though he knew they were illegal. Year after year after year, he kept the public in the dark,” said Damian Williams, the U.S. attorney for the Southern District of New York who is also prosecuting rapper Sean “Diddy” Combs.

Mr. Adams’ ties to foreign figures date to 2014 when he became Brooklyn borough president, the indictment says.

Prosecutors say his decision to run for mayor supercharged ties with Turkish officials, in particular, who offered discounted travel on a Turkish airline and lavish perks in Istanbul and other global hot spots before asking Mr. Adams for favors when he won the hotly contested Democratic mayoral primary in 2021.

Mr. Williams pointed to an alleged episode in which a Turkish official told Mr. Adams that because Turkey supported him for mayor, it was “his turn” to support Turkey by muscling Fire Department of New York officials to approve a skyscraper consulate, known as the Turkish House, despite safety concerns.

“Adams delivered and pressured the fire department to let the building open,” Mr. Williams said. “The FDNY professionals were convinced that they would lose their jobs if they didn’t back down. So they did. They got out of the way and let the building open.”

Mr. Adams, a former city police officer, is charged with bribery and conspiracy to commit wire fraud and receive campaign contributions from foreign nationals.

It is a damaging development for the mayor, who was once hailed as a national model for Democrats. Expectations of charges rose in recent weeks amid the swirl of investigations and resignations that dogged the administration.

Federal agents searched Mr. Adams’ official residence, Gracie Mansion, on Thursday before authorities detailed the charges.

Mr. Adams, 64, said he had no intention of stepping down.

“We are not surprised. We expected this,” Mr. Adams said while smiling broadly at a press conference. “I ask New Yorkers to wait to hear our defense before making any judgments.”

The mayor said he knew the rules and didn’t take foreign donations.

“I look forward to defending myself and the people of this city as I’ve done through my entire professional career,” he said.

Mr. Adams surrounded himself with supporters at the rain-soaked media event. They spoke individually from the lectern while hecklers shouted at the mayor and his friends, creating a raucous and awkward scene.

“You are a disgrace to all Black people in this state. This is ridiculous. You can shush me all you want, but the people are with us,” shouted a man with a megaphone.

At a separate press conference, Mr. Williams and federal agents rejected the idea that Mr. Adams was targeted or treated differently than any other defendant.

They said Mr. Adams accepted more than $100,000 in luxury travel benefits, including upgraded trips to France, China, Sri Lanka, India, Hungary and Turkey, but failed to disclose the gifts. Mr. Adams sometimes paid a nominal fee to hide the fact he received heavy discounts, according to the indictment.

“Adams continued to pursue foreign money in secret well into 2021,” said Mr. Williams, pointing to Turkish businessmen and a government official who offered to funnel money to his campaigns.

Prosecutors said the alleged criminality was compounded by Mr. Adams using illicit donations to attract millions of dollars in public matching funds under New York’s campaign system.

“Adams’ campaigns applied for matching funds based on known straw donations, fraudulently obtaining as much as $2,000 in public funds for each illegal contribution,” the indictment says.

Mr. Adams won a hard-fought Democratic primary three years ago by espousing centrist views on policing and public safety and attracting blue-collar support in the outer boroughs.

In the city’s first brush with ranked-choice voting, he edged out former city sanitation Commissioner Kathryn Garcia by less than 1 percentage point in the final round.

Mr. Adams took office in January 2022 on a pledge to restore public safety and revive New York’s energy. Now, he is the city’s first mayor to face a criminal indictment.

The timing is awkward. The indictment landed while foreign leaders, including Turkish President Recep Tayyip Erdogan, descended on the city for the U.N. General Assembly.

Prominent rivals and state and national Democrats are calling on him to step down before his reelection campaign next year.

“There is simply zero chance that the wheels of government will move forward from this full steam ahead,” said Scott Stringer, a former city comptroller running against Mr. Adams. “Instead, we are left with a broken-down train wreck of a municipal government.”

Other election opponents, including city Comptroller Brad Lander and state Sen. Zellnor Myrie, called for Mr. Adams to resign.

Rep. Alexandria Ocasio-Cortez, New York Democrat, urged Mr. Adams to resign shortly before news of the indictment broke.

Mr. Adams’ “numbers are not good in New York City and he just squeaked by with the ranked-choice voting last time. I’m sure he would get a significant field of challengers, which would happen regardless,” said Lee Miringoff, director of the Marist Poll in New York. “He’s weak politically and now faces the jeopardy of having this investigation and indictment, which is going to cause all kinds of distractions. I think there’s three or four investigations that are occurring, and this is nothing but trouble for him.”

If Mr. Adams steps down, Mr. Williams will schedule a nonpartisan special election for mayor within 90 days.

Mr. Williams is considered more liberal than Mr. Adams, so his rise is appealing to groups on the political left.

“Mayor Eric Adams can no longer govern,” said Ana Maria Archila and Jasmine Gripper, co-directors of the New York Working Families Party. “He has lost the trust of the everyday New Yorkers he was elected to serve. Our city deserves a leader we can trust and who is not engulfed in endless scandals. Fortunately for the people of New York, we have a public advocate who is ready to step in and lend stability to the city in this difficult moment.”