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.
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.