Climate change protesters have attached their own image of "an apocalyptic vision of the future" to the frame of John Constable's masterpiece painting The Hay Wain.
Two Just Stop Oil (JSO) supporters struck central London's National Gallery on Monday, forcing the evacuation of art lovers, tourists and a class of 11-year-old children on a school trip from the room where the painting hangs.
A National Gallery (NG) spokesman said that two people entered Room 34 and "appeared to glue themselves to the frame of The Hay Wain by John Constable (1821)".
The protesters, a man and a woman wearing white T-shirts with the slogan Just Stop Oil, stepped over a rope barrier.
They then placed what looked like a large colour paper print on to the front of the large-scale painting.
Each also placed a hand on the frame of the painting and kneeled beneath it before loudly stating their concerns as visitors were ushered out by security staff.
The male protester, who identified himself as an art lover called Eben, said: "Art is important. It should be held for future generations to see, but when there is no food what use is art.
"When there is no water, what use is art. When billions of people are in pain and suffering, what use then is art."
The Hay Wain, which was painted in 1821, is one of the most popular paintings at the gallery and shows a rural Suffolk scene a wagon returning to the fields across a shallow ford for another load.
Eben said: "We have stuck a reimagined version of the Hay Wain that demonstrates our road to disaster."
JSO said they had created a scene that depicts "the climate collapse and what it will do to this landscape."
The NG spokesman said: "They also covered the surface of the painting with three sheets of what appears to be paper featuring a reimagined version of The Hay Wain.
"The pair appear to be Just Stop Oil activists.
"The room has been closed to the public and police have been called.
"Gallery staff, including members of the conservation team, are also in attendance."
It is the latest demonstration by the group which in the past week has allegedly targeted a Scottish art gallery and stormed Sunday's British Grand Prix.
Five men, aged between 21 and 46, and two women, 20 and 44, were arrested after a track invasion on the opening lap of the race at Silverstone.
The incident was not shown on F1's global television feed, but eyewitness footage emerged of five people - understood to be representing JSO - entering the circuit at the high-speed Wellington Straight. They then sat down on the tarmac.
Five JSO members are also said to have attached themselves to a 19th-century landscape by Horatio McCulloch called My Heart's In The Highlands which hangs in Glasgow's Kelvingrove Art Gallery and Museum.
They are also alleged to have sprayed the group's logo on the walls and floor of the renowned gallery in orange paint.
A Metropolitan Police spokesman said: "At approximately 14:25hrs on Monday, 4 July officers were called to a protest taking place inside the National Gallery, WC2 involving two people."