Anti-Trump protesters gathered outside his Manhattan skyscraper after he jetted into the city without wife Melania from Florida on Sunday.
Mr Trump is expected to stay in the city until Tuesday, although it is not known the reason for his visit.
The crowd outside the Fifth Avenue building where Mr Trump has a penthouse apartment, carried signs that read “Arrest Trump”, “Indict Trump”, and “Florida Man Go Home.”
Since leaving the White House on 20 January Mr Trump has been staying at his Mar-a-Lago club in Florida, but he lived in the 58-floor Trump Tower until he was sworn in as president in 2017.
Mr Trump, who was born and raised in the Queens borough of New York, changed his permanent residence to the state of Florida in 2019, and voted there in the 2020 election.
He was accompanied by secret service agents and NYPD officers as he arrived back in the city in a motorcade at 9pm on Sunday.
His trip comes as the Manhattan district attorney’s office has stepped up its criminal investigation into Mr Trump and the financial dealings at his company.
Watch: New York investigation of Former President Trump's finances leads to Chicago Trump Tower
Former prosecutor Mark Pomerantz, who is known for investigating organised crime cases, has been brought in by district attorney Cyrus Vance to look at the Trump Organization, according to reports.
The investigation is focused on possible bank-related and tax fraud, and the Supreme Court has allowed Mr Vance access to the ex-president’s tax returns, which he fought to keep away from prosecutors.
The tower, which brandishes the former president’s name in gold writing, attracted protests throughout the four years of Mr Trump’s time at the White House.
That included a “Black Lives Matter” mural that was painted on the street outside Trump Tower in July 2020, as New York City authorities criticised Mr Trump’s heavy-handed response to anti-racism protests across the US.
Mr Trump’s return to New York comes a week after he gave his first major speech since leaving office, at the CPAC event in Orlando, Florida.
And it also comes just days after it was reported that both Mr Trump and Melania Trump had received the Covid-19 vaccination in January, but had chosen to remain silent on doing so.
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