Trump, a Republican, has spent most of his time since Election Day in his apartment at Trump Tower on Fifth Avenue, forcing police to work with the US Secret Service to provide intensified security measures in one of the city's busiest neighbourhoods.
The situation is "truly unusual," de Blasio said at a news conference.
Trump has used the tower for years as his primary residence and the headquarters of his global business empire. His presence there while receiving high-profile guests to interview for his administration has caused traffic jams and frustrated commuters and tourists.
De Blasio sent letters to President Barack Obama and Congressional leaders on Monday asking for federal funds to pay for security costs from the Nov. 8 election through January 20, when Trump is to take the oath of office in Washington and become the 45th US president.
The 75-day period puts the daily price tag for the New York Police Department at about $467,000. The figure is about half the $1 million daily tab previously estimated by New York media and cited in a petition by City Council members to Trump last week.
"This is a highly-trafficked, dense urban environment, and one that presents an unprecedented and unique target for potential terrorist activity," de Blasio wrote to Congressional leaders. "No other president in modern history has had his primary residence located in such a densely-populated neighbourhood."
De Blasio said that Congress has reimbursed New York in previous years for costs related to the protection of world leaders, including foreign dignitaries, and major events such as the 2004 Republican National Convention.
The city would continue to seek appropriate reimbursement from the Trump administration after his inauguration, de Blasio said. He said he had already spoken with Trump's nominee for treasury secretary, Steve Mnuchin, about the matter.
Trump's wife Melania and young son plan to remain in New York for the rest of the school year, and Trump is expected to return frequently even after moving to the White House.
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