Two ageing pandas at a Tokyo zoo will be returned to China next month for medical care, the city's governor said, with visitors queuing on Saturday to catch their last glimpse of the couple.

The pandas Ri Ri and Shin Shin arrived at Ueno Zoo in 2011 and were due to stay until February 2026, but Japan and China agreed it would be better for the 19-year-olds to return to their home country.

"Symptoms such as high blood pressure have been observed since two years ago. They're currently taking medication and undergoing tests, but there has been no significant improvement," Tokyo Governor Yuriko Koike told reporters on Friday.

"I know some people will be sad to see them go, but when we think first of the health of the beloved pandas, it would be best to see them off warmly."

A final viewing is scheduled for September 28, but local media reported on Saturday that people were already lining up to get one last look at the pandas.

The pair gave birth in 2017 to cub Xiang Xiang -- the zoo's first baby panda since 1988, who became a massive draw -- as well as twins in 2021.

Many fans shed tears when Xiang Xiang was returned to China last year, and her departure was broadcast live on local television.

The black and white mammals are immensely popular around the world, and China loans them out as part of a "panda diplomacy" programme to foster foreign ties.

There are an estimated 1,860 giant pandas left in the wild, mainly in bamboo forests in the mountains of China, according to environmental group WWF.

And there are about 600 in captivity in panda centres, zoos and wildlife parks around the world.