Climate activist Greta Thunberg detained at demonstration in The Hague

Climate activist Greta Thunberg was detained twice by police at a demonstration in The Hague, the Netherlands, on Saturday.

Thunberg was initially detained and held for a short time by local police along with other protesters who tried to block a major highway into The Hague.

After she was released, Thunberg quickly rejoined a small group of protesters who were blocking a different road leading to the railway station. There, she was detained a second time and driven off in a police van.

Before she was detained, Thunberg told journalists she was protesting because the world is facing an existential crisis.

"We are in a planetary emergency and we are not going to stand by and let people lose their lives and livelihood and be forced to become climate refugees when we can do something," she said.

Activists had been trying to block the nearby A12 highway. That road has been blocked for several hours dozens of times in recent months by activists demanding an end to all subsidies for the use of fossil fuels.

At previous protests police drove detained protesters to another part of town, where they were released without further consequences.

Local police would not comment on individual cases but said everyone who tried to block roads was detained.

Police spokesperson Marieke Maas said they could not say how many people were arrested.