"Stop Trump. Save the planet."

That was a key message of the thousands, if not tens of thousands, who marched in the streets of Brussels on Wednesday as U.S. President Donald Trump arrived ahead of a NATO summit meeting.

"This protest march is directed against Trump and his billionaire cabinet," said event organizers in a Facebook post. "This is a march for peace and against military adventures, for the preservation of our planet and the environment, for the respect for human rights of all humans, for the struggle against sexism, racism, and discrimination."

The "Trump not Welcome" march was backed by scores of civil society organizations from across Europe, including Doctors of the World, Amnesty International, Greenpeace, Friends of the Earth Europe, and Oxfam International.

Protesters were also organizing against NATO's arms race and the Belgian government's austerity policies, according to Brussels Times.

"The government is fighting the poor, instead of fighting poverty," the organizers wrote.

One protester, Indi Orozco, 36, told the Guardian, "I am here for many reasons, too many to say. Everything from the racism towards Mexicans and Muslims to the incompetence of his administration."

Iverna McGowan, the director of the Amnesty International European Institutions Office, added, "From the travel ban, to attacks on women's rights, to the planned Mexican border wall, President Trump has overseen an onslaught of hateful and divisive policies."

Trump will hold his first meeting with NATO leaders since taking office. He repeatedly called the alliance "obsolete" on the campaign trail, but has since backtracked on that sentiment, along with other major pledges and statements.