Activists interrupted a session of the Swiss Federal Assembly on Thursday to call for more action to tackle the climate crisis.

More than 40 campaigners were involved and they sang "Bella Ciao", an Italian song that climate demonstrators have amended the lyrics to.

They also unfurled a large banner saying: "Final Countdown — 16 months left."

"(We) demand from parliament a functioning climate plan for 2020. The situation is clear: 2020 will be the decisive year for our future. There are only a few months left," the Swiss chapter of the Climate Strike group said on Twitter.

The 2015 Paris Climate Agreement included several five-year policy cycles — the first one of which is coming to an end in 2020. Nations were then expected to agree to tougher emissions reduction ambitions for the following two cycles.

The 2020-2030 decade is deemed particularly crucial to keep the increase in global average temperature well below 2°C from pre-industrial levels as mandated by the agreement.

The latest UN Intergovernmental Panel on Climate Change report estimated that global CO2 emissions would have to be cut by at least 45% during that decade in order to limit global warming to below 2°C from pre-industrial levels.

Lawmakers in the assembly have reacted differently to the protest.

Christian Democrat MP Ida Glazmann warned that by interrupting parliament, protesters could "annoy many."

Mattea Mayer, from the Social Democratic Party, posted a video of the protest on Twitter, writing: "The time for nice words is over — now's the time for action."

She later told Euronews: "The climate activists' concern is absolutely justified. The climate crisis is real, we must act now!

"With their protest in the Swiss Federal Parliament, they unequivocally call on parliament to take now measures against climate change.

"Banks and pension funds should no longer invest in oil, coal, natural gas or forest clearing. And there is an urgent need for an investment offensive in climate protection measures, e.g. energy-efficient renovation of buildings, promotion of renewable energies, expansion of public transport and so on."

Bastien Girod, a lawmaker from the Green party, said he does "not understand why some parliamentarians are so upset and see this as the demise of democracy."

"We should be happy that the youth (...) is committed to the future," he added.