The 16-year-old Swede, who sailed across the Atlantic for 15 days to attend the UN climate summit on 23 September, remained silent for most of the event.
She then entered the UN building on the East River in Manhattan, without knowing immediately if she would meet officials.
Stop denying that the Earth is dying!
During the demonstration, the one that pushed hundreds of thousands of young Europeans to parade every Friday under the rallying cry #FridaysforFuture remained silent, leaving other teenagers or students to call for action in the face of the climate emergency, some aimed directly the climate-skepticism of the Trump government.
"Stop denying that the Earth is dying!","Strike with us!", or "We can not stop, a better world is possible!", they especially chanted.
Many young protesters said they had come at least partly to see the young Swede, whose face and braids are now recognizable worldwide.
"When we knew that Greta would be there, we knew we could not miss that. She is our inspiration!"Atara Saunders, 17, an organizer of Friday's protests at her high school in the Philadelphia area, said excitedly.
Gabriel Kunin, a 13-year-old New Yorker, told him he was attending his first climate event.
"I knew there would be celebrities"like Greta," he said.I think it's really a good idea, you have to change something".
The protest was especially worth a try-out before the giant UN parade on September 20, which is expected to put pressure on world leaders attending the 23rd Climate Summit at the Annual General Meeting. of ONU.
Greta Thunberg has also planned to participate and events are planned the same day around the world.