Tokyo's first baby panda in 24 years has died from pneumonia, less than a week after its birth.

Ueno Zoo officials held a news conference announcing the death, saying the cub was found motionless and without a heartbeat on his mother's belly.

"It appears that when the baby was being breast-fed, it may have inhaled some milk into its lung and respiratory organs, which caused the pneumonia," zoo director Toshimitsu Doi said.

They said it was then moved to an incubator, but efforts to revive the baby panda failed.

"It's an animal park, so I've gone through the deaths of many animals, which makes me sad each time. But I feel extremely sad this time, especially because all the staff members were taking so much care of the panda cub, often without sleeping," Doi added.

The panda's parents, Shin Shin and Ri Ri, arrived from China last February, with the birth being the first ever to take place at the zoo after a natural mating, rather than by artificial insemination.