(Updates with comment from foreign ministry, Shanghai resident)
By Casey Hall and Martin Quin Pollard
SHANGHAI/BEIJING, Nov 28 (Reuters) - Shanghai authorities put up barriers on Monday around a city centre area where hundreds of people protested over the weekend against heavy COVID-19 measures, one of several anti-lockdown demonstrations that have flared across the country.
From the streets of Shanghai and Beijing to dozens of university campuses, protesters made a show of civil disobedience unprecedented since leader Xi Jinping assumed power a decade ago, overseeing the quashing of dissent and setting up an extensive high-tech social surveillance system.
"We hope to end the lockdown," said 28-year-old Shi at a candlelight vigil in Beijing late on Sunday. "We want to live a normal life. We should all bravely express our feelings."
There was no sign of new protests on Monday in Beijing or Shanghai. The Public Security Bureau did not immediately respond to a request for comments.
The backlash against COVID restrictions is a setback for China's efforts to eradicate the virus, which is infecting record numbers of people three years after it emerged in the central city of Wuhan.
The zero-COVID policy has kept China's official death toll in the thousands, compared with more than a million in the United States, but it has come at the cost of confining many millions to long spells at home and extensive disruption and damage to the world's second-largest economy.
Abandoning it would mean rolling back on a policy championed by Xi. It would also risk overwhelming the health system and lead to widespread illness and deaths in a country with hundreds of millions of elderly and low levels of immunity to COVID, experts say.
The protests roiled global markets on Monday, sending oil prices lower and the dollar higher, with Chinese stocks and the yuan falling sharply.
Chinese state media did not mention the protests, instead urging citizens in editorials to stick to COVID rules. Many analysts say China is unlikely to reopen before March or April, and needs an effective vaccination campaign before doing so.
"The demonstrations do not imminently threaten the existing political order, but they do mean the current COVID policy mix is no longer politically sustainable," analysts at Gavekal Dragonomics wrote in a note.
"The question now is what reopening will look like. The answer is: slow, incremental and messy."
Late on Sunday, in the commercial hub of Shanghai, where its 25 million people were stuck at home in April and May, protesters clashed with police, with security forces taking away a busload of people.
The BBC said police assaulted and detained one of its journalists covering the events before releasing him after several hours. A Reuters journalist was also detained for about 90 minutes on Sunday night, before being released.
Foreign ministry spokesman Zhao Lijian said the BBC reporter did not identify himself as a journalist. The Shanghai government did not comment.
On Monday, the Shanghai streets where protesters gathered were blocked off with blue metal barriers to prevent crowds congregating. Police in high-visibility vests patrolled in pairs, while police cars and motorbikes cruised by.
Shops and cafes in the area were asked to close, a staff member at one told Reuters.
While China's COVID policy has remained a major source of uncertainty for investors, developments are now also being watched for any sign of political instability, something many investors had not considered in authoritarian China, where Xi recently secured a third leadership term.
Martin Petch, vice president at Moody's Investors Service, said the ratings agency expected the protests "to dissipate relatively quickly and without resulting in serious political violence".
"However, they have the potential to be credit negative if they are sustained and produce a more forceful response by the authorities."
The catalyst for the protests was an apartment fire last week in the western city of Urumqi that killed 10 people. Many speculated that COVID curbs in the city, parts of which had been under lockdown for 100 days, had hindered rescue and escape, which city officials denied.
Crowds in Urumqi took to the street on Friday. Over the weekend, protesters in cities including Wuhan and Lanzhou overturned COVID testing facilities, while students gathered on campuses across China.
Discussion of the protests, as well as pictures and footage, sparked a game of cat-and-mouse between social media posters and censors.
In Beijing, large crowds of peaceful but impassioned people gathered past midnight on Sunday on a city ring road.
Some held blank pieces of paper, which has become a symbol of protest. Some drivers honked their horns and gave the thumbs up.
On Sunday in Shanghai, some protesters briefly chanted anti-Xi slogans, almost unheard of in a country where Xi has a level of power unseen since Mao Zedong's era.
While anger with the COVID rules simmers, some people expressed opposition to people taking to the streets.
"These actions will disturb the public order," resident Adam Yan, 26, said. "The COVID situation is quite complicated. It's best to believe in the government and each to do our best."
(Reporting by Martin Pollard and Casey Hall; Writing by Marius Zaharia and Brenda Goh; Editing by Michael Perry and Tony Munroe)