Halloween revellers throng Shanghai, some wearing costumes seen as a protest to China policies

Celebrations in the Chinese financial hub began on the weekend, culminating on Tuesday in a large crowd of mostly young people that gathered around a popular bar area, according to onlookers and social media posts.

While most attendees did not dress up and many of those who did wore outfits like monsters and superheroes, some attracted attention on social media for costumes such as blue and white hazmat suits that gained infamy in China last year for being used by authorities enforcing COVID-19 curbs known as "dabai".

Almost a year ago Shanghai was the site of historic protests over China's stringent COVID restrictions that spread to several cities and which were later seen as a trigger for the country's sudden lifting of the policy in December last year.

Social media posts from Tuesday and the days before included one of a man donning boards illustrating China's slumping stock market and another dressed up as Lu Xun, a famous author whose works have been popular among Chinese youth as they grapple with historic rates of unemployment.

The man recited a work by the author that urged those "who can speak out to speak out", before he was told to leave by a police officer, the video showed. Reuters was unable to verify the authenticity of the video.

"The 'dabai', COVID-19 testing, A-share market...that Shanghai people dressed up as are all elements that speak to the trauma of the times and traces of history. Once again, entertainment is not superficial, behind it are real life scars," said one user on Weibo on Wednesday.

Public critiques of government policies are rare in China, where authorities have been cracking down on free expression.

Some party goers also showed up with blank sheets of paper stuck to their clothes, a key symbol of last year's protests, other social media posts showed.