UK police Tuesday removed Swedish climate campaigner Greta Thunberg from a protest outside the energy sector's annual London get-together, an AFP photographer reported.

The 20-year-old activist, who has become a key face of the movement to fight climate change, was taken away by two police officers and put into the back of a police van outside the Energy Intelligence Forum.

Joining a mass protest, Thunberg earlier slammed "closed door" agreements struck between politicians and representatives of the oil and gas industry.

"Behind these closed doors, spineless politicians are making deals and compromises with lobbyists from (the) destructive fossil fuel industry," Thunberg told journalists outside the venue hosting the annual gathering, which runs until Thursday.

Several hundred protestors gathered by the InterContinental London Park Lane hotel during the "Oily Money Out" demonstration, organized by pressure groups Fossil Free London and Greenpeace, blocking all entrances to the venue.

The carbon-intensive sector has faced fierce criticism from the green lobby for continuing to invest in dirty fossil fuels and worsen climate change -- instead of accelerating the shift towards cleaner renewable energy.

"The world is drowning in fossil fuels. Our hopes and dreams and lives are being washed away by a flood of greenwashing and lies," added Thunberg.

"It has been clear for decades that the fossil fuel industries were well aware of the consequences of their business models, and yet, they have done nothing.

"The opposite -- they have actively delayed, distracted and denied the causes of the climate crisis and spread doubts about their own engagement in it," she said.