Teenage climate activist Greta Thunberg sailed into New York Harbour on Wednesday in a zero-carbon emissions vessel, completing her 14-day journey from England to take part in a United Nations climate summit in New York next month.

The Swede was met with cheers as she stood on the ship's bow and waved a red flare above her head as it sailed past the iconic Empire State building into North Cove Marina.

"All of this is very overwhelming and the ground is still shaking for me," Thunberg said at a press conference on dry land.

"It is insane that a 16-year-old should have to cross the Atlantic ocean to make a stand," she added, telling the gathered crowd that the "fight across borders" and that "we need to stand together, support each other, and take action, otherwise it might be too late".

You can watch back live footage from her arrival and press conference in the video player here:

The 16-year-old Swede, who set sail from Plymouth, England, on August 14, attracted international attention last year when she started missing school on Fridays to protest against political inaction on climate change, inspiring youth around the world to do the same.

"Land!! The lights of Long Island and New York City ahead," Thunberg tweeted around 4 am EDT (10 am CEST) on Wednesday, posting a picture of tiny dots of light on a dark horizon.

Rather than travel in an aeroplane that burns fuel and contributes to atmospheric carbon pollution, Thunberg opted to make her trans-Atlantic journey carbon emission-free by sailing on the Malizia II, a 60-foot yacht equipped with solar panels and underwater turbines that produce electricity onboard.

The boat has no shower or toilets, and those aboard including Thunberg's father and crew members ate freeze-dried food throughout the trip.

The teenager said she was looking forward to going for a walk and eating fresh vegetables rather than those out of a can after her two-week trip.

Upon arriving in the US, Thunberg's message for President Donald Trump was: "Listen to the science," but she added, "he obviously doesn't do that."

In addition to the UN Climate Action Summit in New York, the activist intends to join the COP 25 climate change conference in Santiago, Chile, in December.

Greta said she would also be travelling to Chile without flying, using trains, buses and possibly another boat.

She added the summits have to be "a breaking point" and that she was "going to do everything I can to make sure world leaders have all eyes on them so they cannot continue to ignore this".

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