Demonstrators in the commercial capital, Shanghai, could be heard chanting, "Xi Jinping! Step down! CCP (Chinese Communist Party)! Step down!"
"I'm here because I love my country, but I don't love my government... I want to be able to go out freely, but I can't. Our COVID-19 policy is a game and is not based on science or reality," said one protester, Shaun Xiao.
Protesters were seen holding up blank sheets of paper at rallies, symbolizing their protest against Chinese censorship.
China reported a fifth straight daily record of new local cases of 40,052 on Monday, up from 39,506 a day earlier.
Police detain protesters in Shanghai
At least two protesters were detained on Monday, the AFP news agency cited their reporters as having noticed police officials leading people away from a protest site in Shanghai.
Protesters rallied amid heavy police presence, while law enforcement officials barred people passing by from taking pictures or recording videos, according to AFP.
Several people were detained and taken away by bus on Sunday as well.
Weibo, China's heavily censored Twitter-like platform, makes no mention of protest rallies in either Shanghai or Beijing.
Dispersed protesters return hours later
Police used pepper spray to drive away demonstrators in Shanghai, but hours later residents returned to the same spot, only for police to break up their protest for a second time.
Video footage posted to social media showed BBC journalist Edward Lawrence being arrested while filming the Shanghai protest.
The footage shows Lawrence being charged at by several officers who then dragged him to the ground before pulling him up with his hands tied behind his back.
The BBC said Chinese police assaulted and detained Lawrence, before later releasing him after several hours.
"The BBC is extremely concerned about the treatment of our journalist Ed Lawrence, who was arrested and handcuffed while covering the protests in Shanghai," a spokesperson for the British public service broadcaster said in a statement.
"He was held for several hours before being released. During his arrest, he was beaten and kicked by the police. This happened while he was working as an accredited journalist," the spokesperson added.
The latest protests erupted after a fire broke out Thursday and killed at least 10 people in an apartment building in Urumqi in the northwestern Xinjiang region, where some people have been locked in their homes for four months.
The tragedy spurred a wave of angry questions online about whether firefighters or people trying to escape were blocked by locked doors or other COVID measures.
In a rare direct challenge to the ruling Communist Party, the demonstrations have spread to at least seven other cities Sunday, including the capital Beijing, Wuhan and Chengdu.
Protests mount over China's 'zero COVID' policy
Blank paper protest in Beijing
In Beijing, a group of about 200 people gathered in a park on the capital's east side and held up blank sheets of paper, a symbol of defiance against the ruling party's pervasive censorship.
About 2,000 students at Xi's alma mater, Tsinghua University in Beijing, gathered to demand an easing of anti-COVID controls, according to social media posts.
Other postings said there were also demonstrations at 50 universities across China.
Wuhan protesters turn violent
In the central megacity of Wuhan, where the coronavirus first emerged, multiple video livestreams showed crowds walking through the streets cheering, but they were quickly censored.
Other footage showed protesters smashing through metal barricades, overturning COVID testing tents and demanding an end to lockdowns.
A large crowd also gathered in the southwestern metropolis of Chengdu, according to videos on social media.
"We don't want lifelong rulers. We don't want emperors," the crowd chanted, in reference to Xi, who has scrapped presidential term limits and could now rule for life.
"I joined the protest because I was dissatisfied with the government's imposition of lockdowns, the government's abuse of power, the strict online censorship, the covering up of truth in the Xinjiang fire and to show solidarity with people in Shanghai," a protester told DW's William Yang.
Another protester said that the lockdown "has been too long and it has cost people their freedom and jobs," which is why he was taking part in the demonstrations.
Others complained government assistance had been scant at a time when people were reaching into their savings to cover expenses like mortgages and cars.
Earlier this week, protests turned violent at the world's biggest iPhone factory in the Chinese city of Zhengzhou.
Social media footage showed workers being beaten by police.
The facility was placed into lockdown last month, with many workers forced to sleep inside for weeks.
China cases low, but reach record high
Beijing has stuck with Xi's zero-COVID policy even as much of the world has lifted most restrictions.
While low by global standards, China's case numbers have hit record highs for days, with 39,506 domestic infections recorded Sunday.
The government has defended the policy as life-saving and necessary to prevent the health care system from being overwhelmed, and has vowed to continue with it.