The police escorted the Buddha down the street, one officer steering him with both hands. They hurried a giant poop emoji out of a cheering dance circle in a public park. They also pounced on Donald J. Trump with a bandaged ear, and pushed a Kim Kardashian look-alike, in a tight black dress and pearls, into a police van, while she turned and waved to a crowd of onlookers.

The authorities in Shanghai were on high alert this past weekend, against a pressing threat: Halloween.

Officials there clamped down on Halloween celebrations this year, after many young people turned last year’s festivities into a rare public outlet for political or social criticism. People had poured into the streets dressed up as Covid testing workers, to mock the three years of lockdowns they had just endured; they plastered themselves in job advertisements, amid a weak employment market; they cross-dressed, seizing the opportunity to express L.G.B.T.Q. identities without being stigmatized.

At the time, many on Chinese social media celebrated the revelries as a joyous form of collective therapy. The Shanghai government even issued a news release saying the celebrations were proof of the city’s “cultural tolerance” and the “wisdom of its urban managers.”

“There is an absence of festivals in China solely dedicated to the simple pleasures of having fun,” it said. “Halloween has filled the void.”

But the authorities have grown increasingly restrictive toward personal expression in recent years, including seemingly apolitical expression. They are also wary of impromptu crowds, especially after the anti-lockdown protests in 2022. And so, for all their praise last year, this year they seemed determined to prevent a repeat.