The de Blasio administration’s top homelessness official abruptly resigned Tuesday, the latest personnel casualty in its struggle to reduce the record-high numbers of homeless people in New York City.

De Blasio said the “changes in structure will begin almost immediately,” including how contracting with nonprofits is done, information is shared across agencies, and how to coordinate and deliver services.

With nearly 60,000 people sleeping in shelters and mounting criticism of the city’s approach from outside and inside the administration, Department of Homeless Services Commissioner Gilbert Taylor told Mayor Bill de Blasio that he would quit by New Year’s Day.

“After careful consideration and deep reflection I’ve decided to leave to pursue new professional opportunities,” Taylor wrote, according to a copy of the resignation letter his agency provided. Taylor, 45, said he’d transition to an advisory role as the administration brainstorms how to handle homelessness.

Speaking at a hastily called news conference in the City Hall rotunda, the mayor would not directly say when asked, twice, whether Taylor was encouraged to go.

“He made clear his interest in looking at other options,” de Blasio said. “It connected with the fact that we had all been talking about some of the changes and reorganization we’d had to consider.”

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Until Taylor’s replacement is hired, Taylor’s responsibilities will be handled by the city’s welfare commissioner, Steven Banks, with help from the first deputy mayor, Anthony Shorris.

De Blasio said Banks and Shorris would oversee a 90-day review process to consider how “to ensure services are delivered as efficiently and effectively as possible in order to prevent, reduce and manage homelessness.”

Taylor’s departure comes months after his boss, Deputy Mayor for Health and Human Services Lilliam Barrios-Paoli, announced in August that she would leave her post.

The growing number of people living in shelters, and the city’s apparent inability to reverse the trend, has become a political liability for de Blasio. Last month, Gov. Andrew M. Cuomo’s spokeswoman said the state would soon step in because “it’s clear that the mayor can’t manage the homeless crisis.” De Blasio’s own police commissioner, William Bratton, said the administration made a “mistake” by failing to recognize that homelessness “has exploded over the last two years.”

The number of homeless people in shelters is more than 59,000, according to the Coalition for the Homeless — an increase from about 53,000 when de Blasio took office in January 2014. The figures don’t include the 3,000 or so who live on the street.

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De Blasio has attributed the homeless problem to the 2008 recession, pricier housing and other economic forces.