Extinction Rebellion protesters have broken into the UK’s largest oil refinery and scaled two 50ft silos where they have locked themselves to the structures.
Early on Thursday morning, the activists cut the site's electric perimeter fences and chained themselves to various structures at the ExxonMobil base in Hampshire.
Some have scaled giant silos and unfurled two banners that proclaim: "Climate Emergency" and "No Future in Fossil Fuels".
The environmental group have claimed to have "shut down" the plant, posting a photograph of activists in a pink boat.
An Extinction Rebellion spokesman said: "Just three days before the COP26 Climate Summit, they are demanding that the UK Government listens to the people and stops all fossil fuel investments now.
"The campaigners also condemn ExxonMobil’s massive expansion of its diesel production facilities at Fawley, despite the International Energy Agency (IEA) warning that all new fossil fuel developments must stop this year to keep the world within safe limits of global heating and meet the goal of net-zero emissions by 2050.
"ExxonMobil has known the devastating effects of fossil fuel production on the environment for over 40 years, but instead of acting responsibly on that knowledge, they've spent tens of millions funding climate denial and misinformation and obstructing a transition to cleaner energy sources.
"Only decarbonisation of our economies will limit the scale of death, destruction and mass extinction that climate change will bring in decades to come, the effects of which are already being felt around the world.
"Extinction Rebellion’s immediate demand to Government is simple - stop all fossil fuel investment now."