The dramatic footage was almost impossible to miss. A torrent of water tearing through Gyirong Port, one of the main border crossings between Nepal and Tibet, sweeping away all in its path as hundreds of people fled for their lives.The scenes, captured by CCTV cameras, quickly spread on social media and onto screens around the world.Except here, in China.Only a single still-frame shot has been broadcast so far by the country's state-run flagship news bulletin.It has also been difficult to find the video on China's heavily censored internet. It is just as hard to even find posts describing the flash flooding that has claimed hundreds of lives, with just as many still unaccounted for since Wednesday.Beijing has launched a massive rescue operation involving hundreds of emergency workers, which is continuing, and President Xi Jinping chaired an emergency meeting with officials to co-ordinate efforts. But when you compare the country's internet content to what much of the world has been seeing online these past few days, China's firewall becomes more visible than ever. Tibet, which Beijing annexed in the 1950s, had long resisted rule by the Chinese Communist Party. China has quashed protests over the years, sometimes violently, and has been accused of grave rights violations in the Buddhist region. It has labelled the exiled spiritual leader, the Dalai Lama, a separatist.That history means the very name Tibet draws China's censors. Beijing's sensitivities are especially apparent at times likes this. On Thursday night, as global headlines led on the devastation in a Himalayan valley, China's state broadcaster opened its main bulletin with the launch of Xi's new book, a selection of his "most important and fundamental works".Foreign journalists cannot travel to Tibet without government permission. We have just a few hours to get as much information as we can on huge stories like this before videos are scrubbed and voices stifled. Instead, we have to rely on state media, which has so far focused on incredibly dramatic rescue efforts.Specialist search teams scaling mountains and cliff faces, or crossing raging rivers to try to get to the worst-affected areas. We don't yet know what happened afterwards, or who they were able to save.This is not to say that Beijing is unconcerned. Rather, they are very concerned.China's Premier Li Qiang was quickly despatched to the region, where he was seen inspecting debris removal - a rare visit by the country's second-most important leader so soon after a major disaster.The reason for what the world might see as a muted response is to preserve the one thing Xi covets for his country: stability.The Communist Party will fear that such a disaster could fuel discontent, either with the response or the lack of foresight to prevent it. It may also fear the impact of a tragedy like this and its potential to be a rallying factor, especially in a community where faith has long played a central role.Although the region has not seen protests in a long time, Tibetan groups abroad have expressed concern over increasing Chinese control, such as new education laws that they say aim to weaken the role of monasteries and the Buddhist faith.Just hours after the disaster struck, the Communist Party machine tried to rally its grassroots to stem any signs of discontent of its handling of the landslide.A notice came from the local party office urging members to step up and help in disaster relief efforts in their area and provide emotional guidance or psychological support to affected residents. The key line instructs them to "make every effort to maintain social order and ensure stability and public confidence in the disaster areas". Those who perform well would be rewarded - and those who do badly "would be held accountable".It is a warning that will not be taken lightly. Tibetans in the region can be detained or arrested for speaking to journalists or posting anything online that is seen as contrary to the government narrative, according to rights activists.That is making it difficult for Tibetans outside the region to find out what has happened to their relatives.The International Campaign for Tibet, while praising the work of first responders in the area, said Beijing had been removing videos and other first-hand information from social media. It called on Chinese authorities to "disclose complete and verifiable information about the damage and casualties".To try to understand what life is like for Tibetans, the BBC travelled to a town that sits on the edge of the Himalayan plateau last year - just outside what China calls the Tibetan Autonomous region.There, we spoke to monks at the Kirti monastery in Aba, or Ngaba in Tibetan, which was once at the heart of its resistance to Beijing. "We Tibetans are denied basic human rights," one monk told us.They said they lived under constant surveillance and claimed the Chinese government oppressed and persecuted Tibetans. The conversations were brief because we could not be seen speaking to anyone for long. Beijing denies it is violating Tibetans' rights, and points to the heavy investments it has made in the region to boost tourism and integrate it with the rest of the country.Nevertheless, people in China will not know very much about what is happening in Tibet right now.