Three existing city jails and one site in The Bronx have been proposed as the new Rikers Island.

Mayor de Blasio on Wednesday announced an agreement with the City Council to open or expand jails in Manhattan, Brooklyn, Queens and The Bronx as part of a plan to phase out the troubled island-based jail in the East River.

Under the deal announced with Council Speaker Corey Johnson, a new jail would be sited at 320 Concord Ave . in the Mott Haven section of The Bronx, where an NYPD tow pound is currently located.

Three existing detention facilities in Manhattan, Brooklyn and Queens would be retrofitted as Rikers replacements.

The sites are: the Manhattan Detention Center at 125 White St.; the Brooklyn Detention Center at 275 Atlantic Ave. and the Queens Detention Center at 126-01 82nd Avenue in Kew Gardens.

The four sites together will provide space for 5,000 inmates.

There are currently 9,000 prisoners on Rikers Island.

“This agreement marks a huge step forward on our path to closing Rikers Island,” said de Blasio. “In partnership with the City Council, we can now move ahead with creating a borough-based jail system that’s smaller, safer and fairer.”

Johnson, the new speaker, pointed out that the Council, under his predecessor Melissa Mark Viverito, accelerated the movement to close Rikers by creating a panel that recommended just such an action.

“Today is a historic day, as we are yet one step closer to closing Rikers Island,” Johnson (D-Manhattan) said.

But not all political leaders were pleased.

Bronx Borough President Ruben Diaz Jr. said he was blindsided by the announcement and the choice of the Mott Haven location for a new jail.

“I hope that, going forward, this lack of outreach is not a harbinger of the amount of community input the people of my borough will have in this process. I expect that the administration will present my office with a detailed outline of their plans for a new jail, and I will examine those plans carefully as the process moves forward,” Diaz said in a statement.

While agreeing that criminal justice reform and a fairer court system to all New Yorkers is a “defining issue of our time,” Diaz added, “any new site for a jail in this borough must be thoroughly vetted, and the people of The Bronx must have a meaningful say in the selection of any future site . . . Presenting the selection of this site as a fait accompli undermines the entire process, and has the potential to derail necessary criminal justice reform.”

Under the agreement, the jail sites will need to undergo public review under the city’s Uniform Land Use Review Procedure – which includes hearings and recommendations by the local community board, borough president, the City Council and the City Planning Commission.

The proposal to renovate, expand or construct jails in Manhattan, Brooklyn, Queens and the Bronx would be rolled into a single ULURP process, which will allow for a speedier review.

An application could be submitted for certification as early as by the end of 2018, and the design process could begin as early as next summer, officials said.

The announcement was made just days after a correction officer was brutally attacked by Rikers inmates, which was captured on videotape. Corrections Officer Jean Roston Souffrant suffered a fractured spine and other injuries. Four of the six inmates were charged following the gang assault.