A Dutch court has ordered the state to slash greenhouse gas emissions by at least 25 percent by 2020, after a group of citizens took their government to court.

Climate activists in the packed courtroom clapped and cheered as presiding Judge Hans Hofhuis read the ruling on Wednesday.

"The court orders the state to reduce the overall volume of greenhouse gas emissions in such a way that they are at least 25 percent less in 2020 compared to 1990," Hofhuis said.

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The ruling came after almost 900 Dutch citizens took their government to court in April in a bid to force a reduction of greenhouse gas emissions to tackle climate change.

Marjan Minnesma, who heads the environmental rights group, Urgenda, which took the case to court, said the group wanted The Hague to reduce greenhouse gas emissions by 40 percent over 1990 levels by 2020.

"The parties agree that the severity and magnitude of climate change make it necessary to take measures to reduce greenhouse gas emissions," the court said in its ruling.

"The state must do more to reverse the imminent danger caused by climate change, given also its duty to protect and improve the environment," the court said.

Effective control of Dutch emissions is "one of the state's tasks", it said, adding that the cost of the reductions would not be "unacceptably high".

European precedent

"A courageous judge. This is fantastic," said Sharona Ceha, another Urgenda worker. "This is for my children and grandchildren."

The Amsterdam-based Urgenda said the case was the first in Europe in which citizens attempted to hold the state responsible for its potentially devastating inaction and the first in the world in which human rights are used as a legal basis to protect citizens against climate change.

The petitioners had asked the judges to rule that a rise in global temperatures over two degrees Celsius would be a human rights infraction.

The international community has agreed to peg global warming to 2C over pre-industrial levels.

Lawsuits against governments and companies have increasingly been seen as a way to press for action against climate change over the past decade.

Countries are to publish their own undertakings to reduce greenhouse gas emissions ahead of a hoped-for global deal to be agreed in Paris in December.

The 28-member European Union has said it will reduce emissions by 40 percent compared to 1999 levels by 2030, while the world's second-largest polluter after China, the United States, has said it wants to reduce emissions by 26-28 percent by 2025.

The Dutch government can appeal the ruling to a higher court.

It remains unclear exactly how the court can enforce its ruling. It has the power to impose fines for failure to carry out its orders, but never uses such powers against the government and Urgenda did not request such a move, said Judge Peter Blok.