Beijing will regard protesters as crossing the red line, causing the halt at Hong Kong International Airport. In a limited but highly public manner, the function and power of the Chinese state have ceased.
President Jinping and his servants believe that the current situation in which flights have been halted for the past two days cannot continue. This is not so much the damage to the Hong Kong economy or the disruption that these protests cause to passengers. This is because the protests are clearly undermining the supreme authority of the Chinese Communist Party.
For the Beijing Standing Committee, this undercutting is extremely intolerable.
This does not mean that China wants to use military force to crush the Umbrella protest movement. Beijing knows that the visualization of the soldiers of the army for the liberation of peoples lining the young protesters will be catastrophic to the international reputation of the regime. This may be seen as a second cruelty on Tiananan Square.
While vicious authoritarianism is the defining feature of the Communist Party of China, Beijing must make a credible claim to the contrary. This claim is crucial if Xi is to succeed in expanding its Belt and Road economic initiative. Finally designed to replace the US-led democratic international order, Belt and Road involves generous Chinese investment abroad in exchange for domination of the Chinese market and feudal political loyalty.
Concerns about Chinese Communists are not nearly as much as the well-understood rule of state power. The principle should be upheld, Beijing believes, to prevent future resistance to the state.
Therefore, Beijing's escalating threats to use force in Hong Kong cannot be dismissed. If protesters continue to shut down Hong Kong International Airport, Xi will deploy troops to crush them.