A baby giant panda died at a Tokyo zoo today, less than a week after becoming the first cub to be born at the facility in 24 years.

Tokyo's Ueno Zoo said the male panda, who had not been named, died of pneumonia.

A keeper found the cub, which was born last Thursday, lying belly up and not breathing, on his seven-year-old mother's chest.

He was pronounced dead an hour later, after resuscitation efforts failed.

In a news conference, Yutaka Fukuda, the zoo's chief panda keeper, said milk had accidentally entered the baby's airway while his mother, Shin Shin, was breast-feeding him. A post-mortem examination found traces of milk in the cub's bronchial tube.

The baby panda had been kept in an incubator for three days before being returned to Shin Shin yesterday.

"They peacefully spent the night and the baby was doing fine just this morning," Mr Fukuda said with tears in his eyes. "It happened so suddenly, and it's such a pity."

The panda was the first to be born at the zoo since 1988 and was conceived naturally. Giant pandas have a low birth rate, and artificial insemination is common in captive breeding programmes.

His mother arrived from China just before Japan's tsunami and earthquake disasters last year.

The much-anticipated baby, the first born to Shin Shin, had been celebrated across Japan, and the news of his death topped TV news bulletins.

The zoo said it would set up a space for visitors to lay flowers and pray for the dead panda.

Fewer than half of newborn pandas survive for more than a week, Mr Fukuda said, citing Chinese panda experts. The rate is even worse for pandas born to first-time mothers, he added.