Protests against China's heavy COVID-19 curbs spread to more cities, including in the financial hub Shanghai early on Sunday, nearly three years into the pandemic, with a fresh wave of anger sparked by a deadly fire in the country's far west.

A fire on Thursday that killed 10 people in a high-rise building in Urumqi, capital of the Xinjiang region, has sparked widespread public anger as many internet users surmised that residents could not escape in time because the building was partially locked down, which city officials denied.

The fire, and a denial by authorities that COVID measures had hampered escape and rescue, has fuelled a wave of civil disobedience unprecedented in mainland China since Xi Jinping assumed power a decade ago.

In Shanghai, China's most populous city, residents gathered on Saturday night at the city's Wulumuqi Road - which is named after Urumqi - for a candlelight vigil that turned into a protest in the early hours of Sunday. As a large group of police looked on, the crowd held up blank sheets of paper - a protest symbol against censorship.

Later on, they shouted, "lift lockdown for Urumqi, lift lockdown for Xinjiang, lift lockdown for all of China!," according to a video circulated on social media.

At another point a large group began shouting, "Down with the Chinese Communist Party, down with Xi Jinping”, according to witnesses and videos, in a rare public protest against the Chinese leadership.

The police tried at times to break up the crowd. China is battling a surge in infections that has prompted lockdowns and other restrictions in cities across the country as Beijing adheres to a zero-COVID policy even while much of the world tries to coexist with the coronavirus.

While low by global standards, China's case numbers have hit record highs for days, with nearly 40,000 new infections reported by health authorities on Sunday for the previous day.

China defends Xi's signature zero-COVID policy as life-saving and necessary to prevent overwhelming the healthcare system.

Officials have vowed to continue with it despite the growing public pushback and its mounting toll on the world's second-biggest economy.

NATIONWIDE ANGER

The next few weeks could be China's worst since the early weeks of the pandemic for the economy and the healthcare system, Mark Williams of Capital Economics said in note last week, as efforts to contain the outbreak will require additional localised lockdowns in many cities.

In the northwestern city of Lanzhou, residents on Saturday night upturned temporary COVID staff tents, smashed COVID testing booths and took to the streets in protest, posts widely shared on China's WeChat, Kuaishou and Weibo social media platform showed.

Protesters said they were put under lockdown even though no one had tested positive. Candlelight vigils for the Urumqi victims took place in universities in cities such as Nanjing and Beijing, with students staging silent protests by holding up blank sheets of paper.

Internet users showed solidarity by posting blank white squares on their WeChat timelines or on Weibo.

By Sunday morning, the hashtag “white paper exercise” had been blocked on Weibo.

Videos from Shanghai showed crowds facing dozens of police and calling out chants including: "Serve the people", "We don't want health code" and "We want freedom”.

Some posted screenshots of street signs for Wulumuqi Road, both to evade censors and show support for protesters in Shanghai.

Others shared comments or posts calling for all of "you brave young people to be careful".

Many included advice on what to do if police came or started arresting people during a protest or vigil.

The Shanghai government did not immediately respond to a request for comment on Sunday. Shanghai's 25 million people were put under lockdown for two months earlier this year, an ordeal that provoked anger and protest.

Chinese authorities have since then sought to be more targeted in their COVID curbs, but that effort has been challenged by a surge in infections as China faces its first winter with the highly transmissible Omicron variant.

On Friday night, crowds took to the streets of Urumqi, chanting“End the lockdown!” and pumping their fists in the air after the deadly fire, according to videos circulated on Chinese social media.

Many of Urumqi's 4 million residents have been under some of the country's longest lockdowns, barred from leaving their homes for as long as 100 days.

In Beijing, 2,700 km (1,700 miles) away, some residents under lockdown staged small protests or confronted local officials on Saturday over movement restrictions, with some successfully pressuring them into lifting the curbs ahead of a schedule.

A video shared with Reuters showed Beijing residents in an unidentifiable part of the capital marching around an open-air carpark on Saturday, shouting“End the lockdown!” The Beijing government did not immediately respond to a request for comment on Saturday.