Officials at the Isabella Stewart Gardner Museum closed its doors unexpectedly Saturday after learning a group of climate activists planned to protest inside the institution.
The protest was timed for the anniversary of the 1990 heist of works by artists including Degas, Manet, Rembrandt, and Vermeer from the institution, according to a statement from the museum. But officials raised concerns that the demonstration would threaten its staff or its collection.
”We were informed that climate activists were planning a protest inside the Museum that could potentially put our community and artworks at risk,” said the statement. “After careful consideration, and an abundance of caution for the safety of our staff, volunteers, visitors and collection, we made the difficult decision to remain closed for the day.”
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The museum is expected to reopen Sunday at 10 a.m.
The closure, which was announced on the museum’s website Saturday morning, forced a few dozen demonstrators with the group Extinction Rebellion to protest along the Fenway instead for about an hour early Saturday afternoon and block access to Evans Way, which runs alongside the museum.
A Boston police cruiser was parked nearby. No arrests were reported, according to Sergeant Detective John Boyle, a police spokesman.
Demonstrators were trying to raise awareness of the threat posed by climate change, and the destruction of many plant and animal species due to the impact from global warming, according to Susan Lemont, who was among the protesters.

They would not have damaged its collection, Lemont said.
“We love art,” she said. “But there is no art on a dead planet.”
The museum, in its statement, pointed to a series of protests around the world that have targeted art museums for the sake of drawing attention to the threats posed by climate change.
In some cases, protesters have vandalized artwork, including throwing potatoes at a Monet in a museum in Potsdam, Germany, and soup onto a Van Gogh displayed in London.
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At the Gardner, demonstrators had planned to use the empty frames left on display following the 1990 theft to exhibit original artworks protesting the mass extinction of animal species due to climate change. Other demonstrators were going to hold a “die-in” in the museum’s courtyard, the group said.
The museum said in its statement that its namesake had envisioned it as a place to share “art community, and conversation.” Isabella Gardner was also an advocate for art and the environment, it said.
But the museum denounced strategies that threatened artwork while protesting climate change.
“While it is our mission to uphold Isabella’s values, we do not support this type of tactic that targets art institutions and could possibly put the Museum’s collection, staff and visitors at risk,” Peggy Fogelman, the museum’s director, said in the statement.
Jule Manitz, one of the protest’s organizers, said Gardner was a feminist who championed causes she cared about, including the environment.
“She would be out with us, standing here,” Manitz said.
Julia Hansen, who was among the protesters, said demonstrators did not want the museum to feel threatened.
“I wish they had not thought we were a threat to the art. We love art. We wanted to use art to convey our message,” Hansen said.
Many visitors to the museum appeared to take its unexpected closure in stride and offered support for the demonstrators’ cause.
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Bethany Jelinek, 23, and Nathan Bowles, 26, had traveled from Dallas to visit friends in the area and had planned to stop in the museum Saturday. They said they understood the museum had to take steps to protect its collection, but supported the protesters and their message.
“This type of activity is effective,” Jelinek said. “It’s nice to hear it’s for a good cause.”
Grace Fleming, 20, a Northeastern University student, brought her grandmother Barbara Fleming of Wisconsin to the museum for a visit. She said she supported the demonstrators, but the protest should not have impinged on the museum.
“I’m kind of surprised. ... It seems unrelated,” Fleming said. “I can support the environment and still look at art.”
Mari Gebremeskel, 29, of East Boston, said the demonstrators had the right to speak out.
“That needs to happen, if anything. Our world is being destroyed,” Gebremeskel said. “I’m all for it.”
John Hilliard can be reached at john.hilliard@globe.com.