"Luckily, nobody was injured," said Westra, adding that the collapse had not damaged the house where Anne Frank and her family had lived in an annexe during the Nazi occupation of the Netherlands until their discovery in 1944.
Anne Frank died in 1945 at the age of 15 at the Bergen-Belsen concentration camp in northern Germany.
She wrote in her diary on February 23, 1944: "The two of us looked out at the blue sky, the bare chestnut tree glistening with dew, the seagulls and other birds glinting with silver as they swooped through the air."
"We were so moved and entranced that we couldn't speak."
The diseased tree had been due to be cut down in 2008 because experts said its mould-infested trunk could snap at any moment, but local residents and tree experts intervened to save it, raising funds for a steel frame.
"When we learned that the tree was diseased, in 2005, saplings were taken and grown to make young trees. Around 100 of them have been offered around the world to be planted," said Westra.
"One of them is in the Anne Frank garden in Paris, and another was sent to the White House," he said.
In 2009, 150 saplings were set aside for planting in a wood in the Dutch city.
Anne Frank's memoir, published in English as The Diary of a Young Girl, is one of the most widely read books in the world. It was found by a family friend after the end of the war.
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