Greenpeace activists have blockaded all entrances to the BP headquarters in London, demanding an end to all new oil and gas exploration.

The campaigners arrived at 3am on Monday and encased themselves in heavy containers before the oil company’s annual general meeting on Tuesday.

The containers, each weighing several tonnes, are being used to blockade all five entrances to prevent staff from entering BP’s offices in St James’s Square.

Two activists are encased in each of the five containers with enough provisions to last at least a week. Another 15 activists are occupying the top of the boxes after abseiling down the side of the building.

Greenpeace said it was carrying out the action because BP was behaving as if the climate emergency was not happening.

The group accused BP of “fuelling” the emergency and called on the company to “end the search for new oil and gas and start a rapid switch to 100% renewables”.

Speaking to the Guardian by phone from inside one of the boxes, the activist Paul Morozzo said: “The situation is so serious so it needs action. We are definitely keen to stay for as long as we can.”

He and his fellow activist Darren Payne are in a box outside the main staff entrance to BP’s offices. He said: “We’ve got food, water, a small Portaloo and some books to read and phone communication. What more could anyone need?”

Morozzo refused to say how the boxes were made or assembled but said they were designed to be impossible to move without harming those inside. “The police can’t move these things without hurting us and they can’t get in without risking us.”

He added: “I’ve been told not to talk about our logistics because it’s useful for us for future actions not to disclose details.” But he said the container was so solid that he could only communicate with fellow activists chained to the top of the box by phone.

“At some point, either me and Darren will fall out, or we will run out of food and water. There’s obviously a physical limit to how long we can stay. It’s highly likely we’ll be arrested eventually.”

Morozzo is a 52-year-old direct action veteran. In 2016 he helped attach gas masks to several statues in London to protest against air pollution, and he was one of 17 campaigners who occupied the top of a chimney of a gas-fired power station in West Burton in Nottinghamshire in 2012.

He said: “We were on top of a chimney for five days so it was quite similar in way. But this is a tiny space with no natural light. There’s some tiny air vents but you can’t really see outside. You can just about stand up and sit down but not much else.”

He added: “One of the activists trained by spending a couple of days studying in a cupboard to get used to it.”

In a statement, Morozzo said: “We’re shutting down BP’s HQ because business as usual is just not an option. BP is fuelling a climate emergency that threatens millions of lives and the future of the living world. The science is clear: we must stop searching for new oil and gas if we want a liveable planet. BP must clean up or clear out.”

The containers feature photographs from Gideon Mendel’s Drowning World project, which looks at the impact of the climate emergency on people worldwide.

A spokesman for Greenpeace said that by 8am on Monday police had attempted to clear the area of pedestrians but had not carried out any arrests. In an email to its employees, BP told head office staff to stay at home on Monday.

Morozzo added: “For too long, BP and the oil industry have paid lip service to climate action while lying and lobbying against it behind the scenes and spending billions scouring the world for more oil and gas. The reality is that BP’s whole business plan is a heavy bet against our hopes to avoid a climate catastrophe and must change.”

Greenpeace claims BP is outspending other oil giants on lobbying campaigns against climate action and spent $16bn (£12.6bn) adding to its oil and gas reserves in 2018. It said only $500m (£392.8m) was invested in alternatives to fossil fuels.

In February, hundreds of environmental activists occupied the British Museum in protest against BP’s longstanding sponsorship of the institution.

The Metropolitan police said officers had been called to the offices just after 4am after reports of protesters scaling the building. A spokeswoman said police were at the scene but no arrests had been made or roads closed.

BP said: “We welcome discussion, debate, even peaceful protest on the important matter of how we must all work together to address the climate challenge, but impeding safe entry and exit from an office building in this way is dangerous and clearly a matter for the police to resolve as swiftly as possible.”