Watch: Protective Prince William keeps his arm around pregnant Kate for New York visit
The Duke and Duchess of Cambridge were greeted with cheers, screams and waves from New Yorkers as they arrived in the US for their three-day visit.
William and Kate are making their first trip to the Big Apple, which has generated huge interest among many Americans.
Around 200 well-wishers gathered on street corners on a freezing night to welcome the royal visitors as they arrived at their plush Manhattan hotel.
Wearing a maroon coat from maternity brand Seraphine to wrap up against the chilly 2C temperatures, Kate, who is five months' pregnant with her second child, looked refreshed despite her long flight.
The royal couple stepped from a large four by four vehicle that was part of a motorcade that had travelled under police escort from John F Kennedy International airport to Manhattan.
William and Kate were accompanied on their scheduled British Airways flight by their private secretaries, senior adviser Sir David Manning, a personal assistant and, brought over privately by the Cambridges, a hairdresser.
Dutiful William stayed close to Kate and kept his arm around her, guiding her through the crowds.
The royal couple had flown first class but their flight was slightly delayed and they arrived around 40 minutes late.
They are staying at the exclusive Carlyle Hotel overlooking Central Park in Manhattan where room prices start at £600 for a stay this week and the top suite is around £10,000 a night.
It was a favourite of William's mother Diana, Princess of Wales and is used today by leading celebrities like Hollywood star George Clooney.
Describing the atmosphere since the visit was announced Danny Lopez, British consul general, New York, said "over the last few weeks there has been incredible interest" and a huge "level of excitement" from people who want to support or be a part of the royal engagements.
As they walked into the hotel Kate and William, both 32, shook hands with the Carlyle's managing director Giovanni Beretta before being taken to their room - a suite with stunning views of Central Park.
The plush 1930s hotel flew the Union flag outside in anticipation of the arrival and the iconic Empire State Building was lit up red white and blue to welcome them.
The building's official Twitter account posted: "We welcome Their #Royal Highnesses the Duke and Duchess of Cambridge by sparkling in red, white @ blue #royalvisitusa."
Inside the Carlyle Hotel, staff were lined up in the lobby and in the run-up to the arrival any guests or members of the public sitting around inside were asked who they were waiting for.
Later tonight William and Kate are expected to attend a private dinner held on behalf of the American Friends of their Royal Foundation.
The royal couple have a varied itinerary tomorrow that will see the Duke meet US president Barack Obama, the couple rubbing shoulders with celebrities at an NBA basketball match and the Duchess visiting a Harlem-based organisation for child development.
The Cambridges will take their court-side seats at the basketball game in the trendy New York suburb of Brooklyn and watch local team the Brooklyn Nets take on the Cleveland Cavaliers tomorrow night.
Seats so close to the action are priced at thousands of dollars but usually cannot be bought as they are prestige places for celebrity supporters like rapper Jay Z and his wife Beyonce.
The Duke and Duchess are both sporty and competitive and are likely to enjoy the spectacle of watching the towering sportsmen.
William will begin his tour today by branding the illegal wildlife trade as one of the most "insidious forms of corruption" in the world.
While Kate will visit the Northside Centre for Child Development in the iconic neighbourhood of Harlem with Chirlane McCray, wife of New York City mayor Bill de Blasio.
The second in line to the throne has been campaigning to save threatened animals for a number of years and will tell delegates at a Washington conference tomorrow some animal parts are worth more then their weight in gold.
William will give a major speech in Washington after meeting the American leader at the White House and vice president Joe Biden.
He is passionate about trying to preserve the planet's most endangered animals and habitats and founded the umbrella organisation United for Wildlife to try and tackle the issue and other problems.
At the World Bank Group's International Corruption Hunters Alliance Conference the Duke is expected to describe the trade in elephants tusks, rhino horns and other animal parts as "one of the most insidious forms of corruption and criminality in the world today".
Highlighting the scale of the problem William will say "some endangered species are now literally worth more than their weight in gold."
William will stress that in China, a huge market for endangered animal parts, the wholesale price of ivory has increased from five dollars (£3) to 2,100 dollars (£1,346) per kilogram in 25 years and poaching has increased as a result.
The Duke will issue a call to action urging the world to act now, saying: "Our collective goal must be to reduce the wildlife trade by making it harder: denying traffickers access to transportation, putting up barriers to their illegal activities, and holding people accountable for their actions.
"Those who look the other way, or spend the illicit proceeds of these crimes, must be held to account."
William will be joined by former foreign secretary William Hague, who hosted the Government's London Conference on the Illegal Wildlife Trade in February, attended by the Duke, Prince Harry and the Prince of Wales, who spoke at the event.
Wildlife crime also poses a threat to world security as it "exacerbates sources of conflict" the Duke will say, and he is scathing about traffickers in animal parts.
"Together they loot our planet, to feed mankind's ignorant craving for pets, trinkets, cures and ornaments derived from the world's vanishing and irreplaceable species," he will say.