They call it the “Blue Great Wall.”

The cobalt-hued metal sheets sprang up just weeks ago across Tianjin, a port city of over 15 million people in northeastern China. They crisscrossed streets and alleyways. They cut off businesses from their customers. They separated neighbor from neighbor.

“From this day forward,” read the signs affixed to many of them, “this residential community will be managed in a closed-off way.”

Barriers of all kinds have sprung up across China. The country is battling the outbreak of a disease called Covid-19, which has killed more than 3,000 people and sickened tens of thousands more. It is caused by a new coronavirus, so named for the spiky protrusions that cover its microscopic surface.

To stop the coronavirus from spreading further, the Chinese government is thinking up new ways to separate its people. Traveling between many of its cities has ground to a virtual halt, freezing large swaths of the world’s second-largest economy.