Police had approved plans by activist group Extinction Rebellion to demonstrate

Hundreds of climate change activists chanting "rebellion!" blocked traffic in downtown Amsterdam on Monday morning, defying a ban by police who said they would make arrests to prevent them from disrupting commuters.

Police had approved plans by activist group Extinction Rebellion to demonstrate on condition they would not block traffic.

The city warned people on their way to work by car and bike to avoid the area because "the police were planning to end the illegal blockade."

"The aim is de-escalation and to break up the blockade and allow for the safe flow of traffic," police said in a statement. "Some demonstrators will be arrested. Police also seized materials that facilitate the demonstration."

Demonstrators gathered on a main traffic artery through the city in front of the national Rijksmuseum with banners that read: "stop talking, start acting" and "tell the truth."

London police detained several Extinction Rebellion activists on Friday before they could carry out a plan to block traffic.