Tuesday was supposed to be a proud moment for China’s leaders, who were celebrating the 70th anniversary of Communist rule. Instead, violence at protests in Hong Kong, including the shooting of a teen by police, provided an ugly reminder of what the regime is really like.

The shooting marked the first time a demonstrator was hit by live ammunition in nearly four months of protests. It was a scene of chaotic clashes, with cops brutally clamping down — using tear gas, water cannons and, in the one case, gunfire. At least 50 other protesters were injured and more than 100 arrested.

And make no mistake: Hong Kong’s cops answer to a local government basically chosen by Beijing.

Meanwhile, officials in the Chinese capital were rejoicing over seven decades of Communist (i.e., totalitarian) control. Beijing’s leaders, including President Xi Jinping, sat overlooking Tiananmen Square — the site of a bloody crackdown 30 years ago — watching a 15,000-troop military parade show off a new ballistic missile. That was followed by a civilian parade, fireworks and musical and cultural performances.

“We must remain committed to the strategy of peaceful reunification and ‘One Country, Two Systems,’ ” said Xi, regarding Hong Kong. “No force can shake the status of this great nation.”

That is, don’t mess with us, protesters.

In recent years, Chinese rule has become increasingly oppressive and riddled with human-rights abuses, particularly against dissenters and minorities, like the Uighur Muslim population.

Hong Kong fears the same fate, especially given the police crackdown. Which, ironically, just reaffirms the need to protest.