A 1,200-year-old calligraphy masterpiece that has been loaned by Taiwan’s National Palace Museum for an exhibition in Japan sparked widespread outrage in China.

The calligraphy, titled “Requiem to my Nephew” by Yan Zhenqing, is considered one of the most precious Chinese treasures dating back to the Tang Dynasty (618-907 AD).

The artwork – which is said to be a draft by Yan Zhenqing and includes his markings and scribbles – was written in 759 AD after the artist learned that his nephew had died. It was preserved in China for centuries and then taken to the Taipei museum in the 1940s when nationalists fled to the island, the BBC reported.

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It is now heading to the Tokyo National Museum for an exhibit honoring Yan's unrivaled work, which the museum said: “reflected the changing consciousness of the times to brilliant effect in his calligraphy.”

Tong Kam Tang, a fine arts professor at the Chinese University of Hong Kong, told the BBC that Yan Zhenqing is a “household name” in China.

“When you’re young and you study Chinese art, you’ll learn [about him],” he said.

It is only the second time the work has been loaned overseas – it was lent to the National Gallery of Art in Washington, D.C., in 1997.

Chinese state media outlet Global Times reported that Yan’s calligraphy has not been displayed in public in 11 years.

However, news of the loan sparked anger among many users on social media site Weibo.

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"Has Taiwan forgotten what Japan did to us? Do they know what the Nanjing massacre is?" one user wrote, referencing the Japanese invasion in 1937 that the Chinese said led to the death of more than 300,000 people.

"This is humiliating. This piece represents the heart and soul of China... and they are sending it to Japan. This is an insult to our ancestors," said another user wrote.

Liu Zheng, a member of the China Cultural Relics Academy, told the Global Times that the relic is in jeopardy while being transported.

“The Chinese mainland prohibits valuable cultural relics, especially paintings and calligraphy, from leaving the country,” Liu said.

The Taipei museum issued a statement assuring people that the masterpiece was “stable and suitable for overseas exhibitions.”

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Taiwan is a self-governed democracy, although China considers the island to be a breakaway province that will one day be fully reunited with the mainland.

Earlier this month, Chinese President Xi Jinping had urged Taiwan to accept that it "must and will be" reunited with China.