Bradley Perrett | Locked down and unhappy, China has been backed into a corner by Xi

Crucially, the grievance is national, not some local dispute like those that often cause isolated ruckuses in China.

The party is no doubt fearing that the whole country will erupt in protests such as it has never faced before, not even in 1989.

It won't lose power, not even if people hit the streets in hundreds of millions. It has always ensured that China has no alternative government. So far as we know, there's not even an alternative to President Xi Jinping and his supporters inside the party.

But we may see the authority of the CCP badly shaken, with a population learning how to tell it to go to hell.

If that happens, everyone in the party will know it's Xi's fault; he could be badly weakened. Ultimately, it has been his decision to insist on only Chinese vaccines, which turn out to be not much good, and to promote distrust of the Western ones that have returned the rest of the world to normality.

So he is the one who has backed the country into a corner, with an endless zero-COVID strategy delivering minimal fatalities and therefore discouraging vaccination by the elderly. China and the CCP have nowhere to go except to maintain rolling lockdowns and wait until adequate domestic vaccines are ready.

Local protests about local grievances are common enough in China. The classic example occurs when rural people are told they'll be thrown off their land without adequate compensation so a developer can build on it.

Everyone assumes, with excellent reason, that the village or town chief has set compensation from the developer at a low level to get a bigger bribe.

There can be disturbances at factories and notably at airports, when, typically, travellers have had enough of hours of delays and the inability of airline workers to tell them when, exactly, they'll be able to get on the plane.

But what we saw last weekend was different. People turned out to protest in many cities at the same time and with the same grievance: they'd had a gutful of being locked up at home, forced to take endless and frequent tests and, in many cases, forbidden to work.

That last problem gets far too little coverage. If you're a Chinese face-to-face worker - say, a gym instructor - you may have pretty ordinary income and not much in the bank. In a lockdown the gym is closed, you're sitting at home eating cheap, monotonous food, and you're not getting paid.

Don't be distracted by excessive media attention on calls for democracy from students at elite universities last weekend. Even if that dream could go anywhere - and it can't - the anger that is really bringing people out on the street is simply frustration with here-and-now hardship inflicted on them.

The protests lasted just two days, and the cops were soon rounding up agitators, to discourage others from taking the lead in future disturbances.

The uni students are important only insofar as they are more likely to protest. On average, they're more idealistic than most people, less busy and, being young and gregarious, less able to cope with lockdowns. So the uni term is ending early and at least one school is paying for train and air fares to send them home - actually, to disperse them.

That still leaves ordinary adult Chinese fed up and sitting in their small flats with grumpy kids. As local lockdowns keep rolling on, the national mood can only worsen from one week to the next. Like furious travellers in an airport terminal, people have no idea when this will end.

So the party must be seeing strengthening conditions for a nationwide explosion.

Crucial to its apparatus of social control is keeping down the number of people who at any given time have gone bolshy. If the street is full of protesters, the cops can't arrest everyone (and don't want to). If people in the next residential compound see what's going on and have the same grievance, they'll come out and join the fun, which is a strong cultural tendency in China.

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The tactic of massing police and flooding them into a disturbed location to intimidate the locals doesn't work if the whole city is on the streets. There aren't enough cops.

If there are too many protests, social-media censors can't keep up with the mass of shared videos. The contagion of unrest can spread from town to town and village to village.

The party then would probably shut down social media, annoying people further. Yet they would still spread the word with phone calls and text messages - unless the party shut down all personal telecommunications. It would if it had to.

Faced with a risk of mass unrest, it is trying mass intimidation. Police are randomly checking phones for unauthorised apps. One aim is to stop people from using foreign messaging services that the party can't monitor. Another is to put everyone on edge, to make them uneasy about disobedience.

The party is also trying to alleviate irritation, telling officials to be less quick to lock down. But the result will surely be more infection and eventually a forced return to harsher measures.

The virus is becoming more contagious and China is heading into winter. This is no time for the party to risk letting COVID-19 get out of control in a weakly vaccinated population.

What a mess it's got itself into.