Protesters from Extinction Rebellion Bristol and Christian Climate Action have blocked access to the Ministry of Defense site at Abbey Wood near Bristol.
Avon and Somerset Police say two protesters, both women in their 70s, have been arrested at one of the entrances for "obstruction of the highway".Protesters held banners with messages including "invest in life not death" during the protest on Friday 11 December.
They wrote on Twitter they want to "highlight the government's distorted spending priorities".
In posts and videos on social media, the group criticised the government's spending commitments on the climate, saying "they have only committed £16 billion to their 10 Point Climate Plan".
They are encouraging supporters who attend the protest to socially distance and bring hand gel and masks. Shortly after 8am, police turned up at the site and could be seen talking to the protesters.
Avon and Somerset Police have told ITV News that officers are at the scene. They warn there may be some disruption while they try to "balance the right to lawful protest with minimising disruption to the community".Reverend Sue Parfitt attached herself to the blockade this morning as part of the demonstration in Stoke Gifford, Abbey Wood.
She said: "Time is running out.
"We have to take extreme measures. The reason we're here is because the military's emissions produce an enormous amount of toxins and its warming the planet.
"At this time, it's the anniversary of the Paris Agreement which was an agreement to keep the planet from warming.
"But our carbon emissions have gone up enormously every year, so we're not anywhere near on target."