Flights and trains to the capital have been cancelled as soon as a region reports COVID-19 cases. And anyone who still makes the journey has to provide a negative PCR test.

But now there's a fortress within Beijing - the Olympics themselves.

Read more: Parts of Beijing sealed off after two cases found - a week before city hosts Winter Olympics

The "closed-loop" system means the Olympics venues are now entirely separate from the rest of Beijing. In effect, there is a city within a city.

The barriers are formidable - COVID Checkpoint Charlies, manned by police and healthcare workers in full PPE.

Buses shuffle athletes and other attendees between the venues.

Officials have even warned Beijing residents not to come to the aid of any Olympics vehicles involved in accidents (this is a city of fender benders at the best of times).

It is less about keeping the athletes safe from COVID than protecting Beijing. There have been more cases already from inside the loop than out.

But those few cases mean the city is anxious. Several districts have been locked down over recent weeks and millions have been tested.

Most people I know have bought enough dried, tinned and frozen food to last a few weeks.

We all watched the harsh lockdown in Xian, where starving residents begged authorities for something to eat, or were beaten by officials for venturing out to find it themselves.

You could get unlucky even if your district remains COVID free - the anxiety is that your health code, an app on your phone that tracks your location history and is required for entry to any public venue, whether it's a supermarket, restaurant or park - goes from green to yellow, or even red, notifying the authorities.

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This is China's "dynamic zero COVID" policy in action. Much of the rest of the world may be scratching its head, wondering how two years into the pandemic China is still using the same tactics as at the beginning (the dreadful coverup and mismanagement of the initial outbreak in Wuhan aside).

But China will not abandon the policy soon and certainly not now, with the Olympics at hand.

This was always going to be a different Winter games - one where the snow is almost entirely artificial, one boycotted by several Western governments.

COVID is another complication. But like the others, China is determined to brush it aside.