Police have tightened security in major Chinese cities after a weekend of protests against pandemic measures.

People took to the streets to voice anger over China's zero-COVID policies. They include tough restrictions on people's movement when infections are detected. Some have spent months at home under lockdown.

Experts like Korogi Ichiro say it is becoming harder for Beijing to defend the rules -- especially with major public events happening abroad -- like the FIFA World Cup.

Korogi, a professor at the Kanda University of International Studies, said, "People watching the matches must have noticed spectators not wearing masks, and cheering without social distancing. They realize COVID lockdowns are not being imposed outside China."

He says Chinese authorities may soon tighten controls over social media and public gatherings.

The US says it stands by the people of China's right to make their voices heard.

US National Security Council spokesperson John Kirby said, "We're watching this closely, as you might expect we would. And, again, we continue to stand up and support the right of peaceful protest."

Despite the unrest, Beijing has defended its strategy.

That includes requirements for people to provide negative PCR tests - to go to the grocery store.

Chinese Foreign Ministry Spokesperson Zhao Lijian said, "Beijing's science-based prevention and control measures have been proven effective. This is a fact witnessed by the international community. Any rights and freedoms must be exercised within the framework of the law."

On Monday, China confirmed 37,000 new cases nationwide. That is down from the country's all-time high of roughly 39,000, which was reported on Sunday.