German police on Wednesday raided homes of climate activists known for their controversial street blockade protests that Chancellor Olaf Scholz has blasted as "completely nuts".

The raids were ordered in an investigation targeting seven people aged 22 to 38 of the Letzte Generation (Last Generation) group, as Germany toughened its stance against their eye-catching action.

From glueing themselves onto the asphalt to flinging mashed potatoes on paintings in museums or blocking airport runways, the activists have in recent months split public opinion with their protests to push the government to do more for the climate change.

Wednesday's raids were ordered over suspicions that the activists were "forming or supporting a criminal organisation", said a joint statement by Bavaria's police and prosecutors.

Fifteen properties were searched, two accounts seized and an asset freeze ordered.

The suspects are accused of "organising a donations campaign to finance further criminal acts" for the group via its website.

At least 1.4 million euros ($1.5 million) had been collected in the campaign, said the authorities, adding that "these funds were according to current information mostly used for the committing of further criminal action of the association".

The authorities did not specify the "criminal action" they were referring to but said two of the suspects are alleged to have tried to sabotage an oil pipeline between Trieste, Italy, and Ingolstadt, Germany, deemed "critical infrastructure" in Bavaria.

At a press conference following the raids, the activists said they would not be cowed.

Spokeswoman Aimee van Baalen admitted that she was terrified when she learnt about the raids targeting her friends.

"They frighten us, but we must not persist in this fear. The government is steering us into a climate hell with our eyes wide open," she said.

"We must continue our resistance," she said, calling a demonstration next Wednesday.

- 'Irritate people' -

Dozens of climate activists from the group have found themselves before the courts in recent weeks over their traffic blockade actions.

Most have received fines for disrupting traffic or obstructing police work but some courts have begun toughening their sentences to also hand down jail time.

Scholz and his coalition partners including the Greens have also expressed frustration at the activists.

Vice Chancellor Robert Habeck of the Greens has said the street blockades were "not a helpful contribution to climate protection" because they don't win consensus but they "irritate people".

Scenes of angry motorists shouting at the glued activists or dragging them off the streets have accompanied many of the street blockades.

The activists argue, however, that their protests are vital in the face of inadequate action taken by the government and society in general to protect the environment and prevent catastrophic global warming.

"We, who are alive today, are the last who can still hinder the irreversible collapse of the climate," the group said.

Berlin has relatively ambitious climate targets, including plans for carbon neutrality by 2045. It is also aiming to produce 80 percent of electricity from renewable sources by 2030.

But Letzte Generation believes that that would be too late to stop Earth from tipping into irreversible warming.

Besides Letzte Generation, Germany has seen a host of other climate activist groups carrying out audacious protests in the last years.

Another group, Scientist Rebellion, hurled cake at Volkswagen bosses at the German carmaker's annual shareholders' meeting earlier this month.

Across Europe, dramatic action has also become more frequent.

On Tuesday, protesters briefly disrupted air traffic at Geneva airport while dozens of activists blocked a business jet convention taking place nearby.

On Sunday, Letzte Generation activists turned Rome's famous Trevi Fountain black, saying that floods that have killed 14 people in the country's northeast were "a warning".