Greta Thunberg sails into New York harbour aboard the Malizia II, on Wednesday. AP
Thunberg, 16, and her crew were expected to arrive at a lower Manhattan marina in the afternoon after a two-week crossing from Plymouth, England.
As the social media-savvy teenager approached New York Harbour before dawn, she tweeted her excitement, saying: "Land!! The lights of Long Island and New York City ahead." The vessel then anchored off Coney Island, so those aboard could go through customs and immigration procedures.
Before setting sail again towards Manhattan, Thunberg waved to nearby boats, including one with journalists tracking her arrival.
The teenager refused to fly because of the carbon cost of plane travel. A 2018 study said that because of cloud and ozone formation, air travel may trap two to four times more heat than that caused by just emissions of carbon dioxide and other greenhouse gases.
The sailboat's onboard electronics are powered by solar panels and underwater turbines.
Thunberg has become a symbol of a growing movement of young climate activists, leading weekly protests in Sweden that focused on the issue and that inspired similar strikes in about 100 cities worldwide.
She's in New York to speak at the United Nations Climate Action Summit next month. There, she'll join world leaders who will present plans to reduce greenhouse gas emissions.
Greta Thunberg sails into New York harbour aboard the Malizia II on Wednesday. AP
The boat carrying Thunberg, the Malizia II, encountered rough seas that slowed it down for a day. Taking turns steering the 60-foot (18-meter) racing yacht were yachtsman Boris Herrmann and Pierre Casiraghi, the grandson of Monaco's late Prince Rainier III and American actress Grace Kelly.
Inscribed on the boat's sail are the words "FridaysForFuture" under "UNITE BEHIND THE SCIENCE."
This was no pleasure cruise. The Malizia is built for high-speed, offshore racing, and weight is kept to a minimum. There is no toilet or fixed shower aboard, no windows below deck and only a small gas cooker to heat up freeze-dried food.
Thunberg, the daughter of an actor and an opera singer, became a European celebrity last year when she refused to go to school in the weeks before Sweden's general election to highlight the impact of climate change.
She continued her school strike on Fridays after the election, spurring thousands of young people to follow suit. Since then, she's met the pope, spoken at Davos and attended anti-coal protests in Germany.
She is now taking a year off school to pursue her activism.
The activists drove up to the British Treasury in a fire engine and sprayed red paint through the hose onto the building, though at one point they lost control of the hose.
Now to collect data that can help presage drastic weather changes and keep people abreast of research in climate change, Air New Zealand is converting one of its domestic aircraft into a flying environmental monitor as part of a world-first project with Nasa.
While most of her peers are preparing for university or enjoying summer vacation, 17-year-old Howey Ou is braving intimidation and criticism in China to save the world from climate catastrophe.
At least 40 people were dead and scores were missing after deadly landslides triggered by heavy rain from the typhoon
Some students sympathetic to Thai protesters said on Friday they were boycotting graduation ceremonies led by King Maha Vajiralongkorn in a show of anger at the monarchy amid growing calls to reform it.
The police have asked parents to pay attention to their children when they approach windows and balconies.