BANGKOK (AP) — A giant panda on long-term loan from China died in a zoo in northern Thailand on Wednesday, six months before she was due to return home, officials from the Chiang Mai Zoo said.

The cause of Lin Hui’s death was not immediately clear but she appeared to have become ill Tuesday morning, and her nose was seen bleeding when she laid down after a meal, said Wutthichai Muangmun, the zoo director.

She was rushed into the care of a joint Thai-Chinese veterinarian team but her condition deteriorated and she died early Wednesday morning, he said.

Tewarat Vejmanat, a veterinarian who spoke at a news conference broadcast live on the zoo’s Facebook page, said the panda, who had a health check every day, was already at an advanced age at 21, and there had been no sign of illness or any difference in her behavior before she became sick.

“China is saddened by the death of the giant panda Lin Hui,” Wang Wenbin, a Foreign Ministry spokesperson, said in Beijing.

Wang said that after China learned about the panda's illness it “immediately organized experts to guide the Thai side to carry out rescue work through video link, but unfortunately did not save her life." He added that the Chinese authorities would soon set up a team of experts to carry out a joint investigation into the cause of death.

Lin Hui’s male mate, Chuang Chuang, who was kept with her at the Chiang Mai Zoo, died there in 2019 at the age of 19. The couple arrived in Chiang Mai in 2003 on a 10-year loan that was later extended for another 10 years.

While the loan was ostensibly for research and conservation purposes, it was generally regarded as an act of friendship by China, which has sent pandas to many countries in what is regarded as a striking example of soft power diplomacy.

When Chuang Chuang died in 2019, Thailand's then-Environment Minister Varawut Silpa-archa said the country had to pay $500,000 to the Chinese government in compensation. It was later reported that heart failure was the cause of his death.

Zoo director Wutthichai said the zoo has a 15-million-baht ($435,000) insurance policy on Lin Hui, who was due to be returned to China this October.

Lin Hui and Chuang Chuang had a daughter, Lin Ping, in 2009 through artificial insemination. A scheme to encourage them to mate naturally by showing them videos of pandas having sex made headlines in 2007. Lin Ping was sent to China in 2013 in what was initially said to be a one-year visit for her to find a mate, but has remained there.

The life expectancy of a giant panda in the wild is about 15 years, but in captivity they have lived to be as old as 38. Decades of conservation efforts in the wild and study in captivity saved the giant panda species from extinction, increasing its population from fewer than 1,000 at one time to more than 1,800 in the wild and captivity.

A Chinese influencer living in Thailand who identified herself as Shanshan visited the zoo Tuesday morning and posted several videos of Lin Hui on the Chinese social media platform Douyin. One of them showed her nose, which appeared bloody, and a red spot could be seen on her neck. In another clip, she was lying down while licking her nose, and there were red stain trails on a concrete slab beneath her head. Screenshots from the videos were widely shared by Thai social media users.

“This is when we just got here, she was lying on her side. Then I saw her nose was bleeding,” she commented in one of the clips. “She looked like she had nausea. We were not sure.”

Screenshots from the videos were widely shared by Thai social media users.

The cause of Lin Hui’s death will take time before it can be determined, Wutthichai said, and how and when that would be revealed will be entirely up to China. Under an agreement between the zoo and the Chinese government’s panda conservation project, an autopsy cannot be performed until a Chinese expert is present.

Some Thai internet users speculated that air pollution in northern Thailand, which in recent weeks has spiked to levels considered dangerous to human health, contributed to Lin Hui’s death. The zoo staff, however, said that was unlikely, as Lin Hui lived in a closed space in an area of the zoo considered to have “the cleanest air.”