Police in Helsinki have warned the public that large-scale protests by climate activist group Elokapina will cause "significant and prolonged" disruption to traffic and public transport services this week.

Elokapina plans to kick off what it calls a "wildfire rebellion" with a demonstration that starts at 3pm on Monday, moving from Senate Square in the centre of the capital to the Finnish parliament on Mannerheimintie.

On a website specially created for the event, the climate group — which is the Finnish branch of the Extinction Rebellion civil disobedience movement — said they plan to remain on the streets of Helsinki for at least three days.

"By concentrating our power at the capital's key nodes, we will amplify our collective voice so powerfully that it can no longer simply be ignored. To create real pressure, we will take control of urban space in spectacular street occupations stretching over several days," Elokapina states.

As of Monday morning, some 1,500 people have signed up to participate in the protests over the course of this coming week — with over 400 saying they are prepared to be detained by police. This number, the group notes, would exceed the Helsinki region's total detention capacity.

"When there are hundreds of us to be arrested at the same time, we can stay on the streets for a long time, generate the necessary public discussion and bring our demands to the nation's highest political tables," the group added.

The purpose of the demonstration, Elokapina said, is to draw attention to "climate collapse", calling on the Finnish government to cut "environmentally and climatically harmful subsidies".

In their own press release, Helsinki police advised commuters to allow plenty of time for travel in the centre of the city, noting further that they "may have to take demonstrators into custody".

Chief Superintendent Jarmo Heinonen of the Helsinki Police Department confirmed this in an interview with Yle on Monday morning.

"If the demonstration is not carried out in accordance with the law or the demonstration causes unreasonable inconvenience, the police will restore normality in accordance with the law. In this case, it means that people sitting on the street will be apprehended," Heinonen said.

In reply to a question about Elokapina's stated aim of testing the police's detention capacity, Heinonen said it was "an odd objective for any demonstration".