Today, President Xi Jinping will preside over elaborate festivities in Beijing to commemorate the founding of the People’s Republic of China. But in Hong Kong, where it is also a public holiday, workers and students are expected to hold antigovernment demonstrations intended to draw the world’s attention away from the mainland.

What to expect: A military parade of 15,000 soldiers and sailors, 160 aircraft and 580 tanks and other weapons will roll through Tiananmen Square. The display is intended to underscore how far the Communist Party has come since taking power — its first parade was said to include 17 planes that flew by multiple times to make its forces seem bigger.

Mr. Xi, the most powerful Chinese leader in decades, is also expected to give a speech this morning, which experts will parse for any references to the political turmoil in Hong Kong.

The latest in Hong Kong: The city is in lockdown mode as it braces for what could be an escalation of protests. The annual fireworks display has been canceled, the morning flag-raising ceremony no longer has a public viewing area, and some malls will be shuttered for the day.

As with previous demonstrations, the protests could become violent. News reports suggest that the police will be deploying as many as 6,000 officers and that China has quietly doubled its military presence in the city.