The first Siberian tiger cub to be found in the wild in China in at least 20 years has died less than two days after being discovered, the Guardian has learned.

Authorities have covered up the death, which casts a shadow over what is potentially the best conservation news the country has had for decades.

It also raises questions about the handling and timing of the discovery, which comes as China celebrates the start of the lunar year of the Tiger and a major financial push to save the biggest cat on the planet.

Early on the morning of 25 February, Han Deyou, a forester in the Wanda mountains in the northern province of Heilongjiang claimed to have discovered a wild tiger cub trapped in a pile of firewood in his yard.

Afraid of its roars and aggression, he called local police and forestry officials, who fed the captive animal beef and chicken as they waited for wildlife experts from a tiger breeding centre to arrive in the remote area the following morning.

The tiger was anaesthetised with a dart, taken away and detained in the jail of the local public security bureau. Experts confirmed it was a Siberian tiger, weighing 28.5kg and thought to be about around nine months old.

Regional media said the cub had probably sought shelter after being separated from its mother in the unusually deep winter snows.

Local authorities hailed the discovery as an "explosively" important development, according to the Northeast China Net website.

There are only about 20 tigers left in the wild. According to regional media, no cubs have been found since the founding of the People's Republic of China more than 60 years ago, though conservationists say records are unreliable before the 1990s.

Although China's wild tiger population is tiny, thousands of the animals are bred in captivity each year. Forestry bureaus are responsible for conservation and receive the bulk of funds related to this end.

The discovery of the young tiger appeared to show that the animals were still breeding in the wild, the best possible news at the start of a year in which the government, World Bank and conservation groups plan to invest heavily in a new programme to save the biggest cat on the planet.

But the case has been quickly shrouded in mystery, tragedy and secrecy.

Ma Hongliang, the propaganda chief of The East Is Red Forest Bureau, told the Guardian that the cub is dead, but the news has been withheld. He has advised Central China Television and other domestic journalists not to report the death because of possible negative publicity.

He declined to answer questions about the time and cause of death. "Experts tried their best to save the cub," he said. "It was too weak to survive."

The full details of the case have yet to emerge. It could yet prove a sad, but essentially positive indication of the potential for the remaining wild tiger population to breed.

Alternatively, it may raise fresh doubts about eco-fraud among a public that has become cynical about conservation claims. In 2008, forestry officials in Shaanxi province endorsed a photograph of a South China tiger, which suggested the animal – until then assumed extinct – was still alive. It was quickly proved a fake.

The financial incentives for such duplicity are substantial because the existence of wild tigers improves the prospects for tourism and the possibility of conservation funds.

But conservation groups said there was reason to believe the latest case may be genuine.

"From the information we have, I think it might be real," said a conservationist, who declined to be named. "This area has been monitored for a long time. Locals have previously reported seeing a tiger and a pup."

Last year, a dead female tiger was found trapped in a snare. The trapper – a frog farmer – was caught. It is not likely to be the mother of the dead cub because tigers are dependent on their mothers for two years.

But conservationists were upbeat about the prospects for more cubs next year if the mother can avoid snares.