Mamdani pledges left-wing success after taking office

Zohran Mamdani has promised to show left-wing politics can succeed as he took over as New York mayor for a term sure to see him cross swords with US President Donald Trump.

Thousands of people gathered in freezing conditions in the United States' largest city to celebrate the 34-year-old Democrat's inauguration after his impressive political rise from relative anonymity just a year ago.

"They want to know if the left can govern. They want to know if the struggles that afflict them can be solved," Mr Mamdani said outside City Hall.

"We will do something that New Yorkers do better than anyone else: we will set an example for the world," he added in a 24-minute speech.

Mr Mamdani, New York's first Muslim mayor, emphasised the cost of living issues that were central to his mayoral campaign, as he promised to help those "betrayed by the established order".

Left-wing allies Senator Bernie Sanders and congresswoman Alexandria Ocasio-Cortez also delivered remarks in front of some 4,000 ticketed guests.

Thousands more people thronged downtown Manhattan, many wearing yellow and blue hats emblazoned with 'Zohran', to watch Mr Mamdani's ceremony on large screens.

It remains to be seen if Mr Mamdani, a self-described democratic socialist, can deliver on his ambitious agenda, which envisions rent freezes, universal childcare and free public buses.

Once an election is over, "symbolism only goes so far with voters. Results begin to matter a whole lot more," New York University lecturer John Kane said.

How Mr Trump behaves could be decisive.

The Republican, himself a New Yorker, has repeatedly criticised Mr Mamdani, but the pair held surprisingly cordial talks at the White House in November.

But one flashpoint might be immigration raids as Mr Trump wages an expanding crackdown on migrants across the United States.

Mr Mamdani has vowed to protect immigrant communities.

Before the November vote, the president also threatened to slash federal funding for New York if it picked Mr Mamdani, whom he called a "communist lunatic".

The mayor has said he believes Mr Trump is a fascist.

Mr Mamdani's inauguration was packed with symbolism. New York Attorney General Letitia James, who successfully prosecuted Mr Trump for fraud, performed a private midnight swearing-in at an abandoned subway station.

Mr Mamdani's office said the understated venue beneath City Hall reflected his commitment to working people.

And in a first for the city, Mr Mamdani used korans to be sworn in as mayor - two from his family and one that belonged to Puerto Rico-born black writer Arturo Schomburg, The New York Times reported.

The new job comes with a change of address as he swaps his rent-controlled apartment in the borough of Queens for Gracie Mansion, the luxurious mayor's residence on Manhattan's Upper East Side.

Some had wondered if he would move to the official mansion given his campaigning on affordability issues. Mr Mamdani said he was doing so mainly for security reasons.

Born in Uganda to a family of Indian origin, Mr Mamdani moved to New York at age seven and enjoyed an elite upbringing with only a relatively brief stint in politics.

Compensating for his inexperience, he is surrounding himself with seasoned aides recruited from past mayoral administrations and former US president Joe Biden's government.

Mr Mamdani has also opened dialogue with business leaders, some of whom predicted a massive exodus of wealthy New Yorkers if he won. Real estate leaders have debunked those claims.

As a defender of Palestinian rights, he will have to reassure the city's Jewish community - the largest in the US - of his inclusive leadership.

Recently, one of his hires resigned after it was revealed she had posted anti-semitic tweets years ago.