Leonardo DiCaprio, Stevie Wonder, Michael Douglas and other stars pleaded for peace and the survival of the planet Friday which Secretary-General Ban Ki-moon said is "closer to conflict than we may like to think."

At a ceremony Friday to commemorate the International Day of Peace on Sept. 21, Ban urged all combatants to lay down their arms that day. And he rang the Peace Bell presented to the United Nations by Japan to "sound a call for peace and a day of non-violence."

The secretary-general enlisted five U.N. Messengers of Peace — DiCaprio, Wonder, Douglas, Japanese violinist Midori, and primatologist Jane Goodall — as well as Nobel Peace Prize winners Shirin Ebadi, Leymah Gbowee and Tawakkol Karman to urge an end to fighting and preservation of the planet.

DiCaprio, who focuses on climate change, showed a short clip from his upcoming documentary on the environment, "Before The Flood" to several hundred young people at the student observance of International Peace Day. It also stars the secretary-general and he said it will be in theaters on Oct. 21.

The Academy Award winning actor said he has witnessed "unimaginable human-caused devastation across our planet." He said the potential of hundreds of millions of climate refugees would create "a future that would be anything but peaceful."

DiCaprio said it was terrifying, but he said "the solutions are available ... today if we begin to make real progress right now." He urged the students to hold their leaders accountable for the promises they made in last December's Paris agreement to combat climate change — and to vote for leaders who focus on renewable energy and "respond before it's too late."

Wonder, who focuses on people with disabilities, spoke about his mother's anguish at his being blind and how he told her maybe God had something greater for him to do than to see, "and I'm so thankful that I was blessed with the gift of song and music."

"Go forward in the struggle for peace with passion and compassion," he said. "The future of this world is in your hands ... You can do well in this life if you do good. Love your family first. Take care of your body and mind. And use God's given talent to make a difference."

Douglas, who focuses on disarmament and emceed the student event, spoke of the dangers of weapons of mass destruction to the planet's survival.

"An overarmed world is an unstable and insecure one," he said. "Disarmament is critical to creating a safer, more prosperous, more equitable and more peaceful world."

Goodall, who focuses on the environment, said her happiest days were studying chimpanzees in Tanzania and she told the students she brought a greeting from them.

"Oah-oh-oh-oh-oh! AH!! AH!!! AH!!!! AH!!!!," she howled to loud applause. "That's hello everybody!"

Goodall noted that the DNA of chimpanzees is only one percent different from humans — but humans are "so arrogant" that they think they're the only beings that matter when, in fact, they "have been destroying the planet that we all call home."

"We need to learn to live in peace and harmony with each other," she said. "And we need to learn to live in peace and harmony with mother nature."

Ban, who grew up during the 1950-53 Korean War, said that conflicts around the world are driving millions of families from their homes, depriving children of an education and subjected many to abuse and exploitation.