BRUSSELS (Reuters) – Tens of thousands of people marched peacefully on Sunday in Brussels urging governments to respect commitments on countering climate change as a United Nations conference on keeping global warming in check opened in Poland.

Belgian police said some 65,000 people participated in Sunday’s “Claim The Climate” demonstration, many of them on their bikes.

Belgium’s liberal Prime Minister Charles Michel called the march “a formidable success” and promised to defend “ambitious targets” at the two week-long U.N. climate change summit which opened on Sunday in the Polish city of Katowice.

Demonstrators marched through the quarter of the Belgian capital that houses the headquarters of the European Union, with banners bearing slogans including “There is no planet B” and “Climate First, Politics Second”.

The organisers called for ambitious climate policies to limit global warming to 1.5 degrees Celsius in line with goals set by the Paris Agreement in 2015.