BEIJING (AP) — China’s internet censors moved quickly to scrub social media posts Thursday after reports that banners criticising the Communist leadership were hung from a busy intersection in the capital Beijing.

Images on Twitter, which is blocked in China, showed smoke spiralling up from a fire on an elevated roadway and banners calling for an end to the hard-line “zero-COVID” policy and the overthrow of Communist Party leader and President Xi Jinping.

Political protest is rare in China, and police are on high alert this week in the run-up to a major Communist Party congress that opens Sunday.

There were no banners hanging from the roadway later in the day, but a circular black scar was visible on the shoulder area where the fire would have been.

It was not clear who might have hung the banners or when they were placed.

Dozens of police milled about the area, entering stores. At times, they stopped pedestrians and questioned them. Associated Press journalists were questioned three times and asked to produce identification. Police denied anything unusual had happened in the area.

Three shopkeepers also denied seeing any banners, smoke or any unusual activity. One woman shook her head “no” without even looking up from her sewing machine.

But a cyclist waiting at a stoplight was overheard saying that traffic was clogged in the area in the morning and smoke was billowing from the bridge.

Posts containing the hashtags Beijing or Haidian were quickly blocked on China’s popular Weibo social media platform. Some of the posts expressed support and praised the unidentified person’s courage without referring to the incident directly.

Others said on Twitter that their accounts had been temporarily disabled on another major Chinese platform, WeChat, after they shared photos of the incident. A song named “Sitong Bridge,” the name of the section of elevated roadway where the incident reportedly happened, was removed from online music platforms.

Xi, who came to power in 2012, is expected to receive a third five-year term as party leader at the end of the congress.

His government’s strict anti-pandemic policy, which has placed millions of people under quarantine, has prompted small protests and confrontations with authorities.

China has the world’s largest online population, building a reliance on the web for shopping and entertainment even while authorities carefully track commentary and quash any criticism of Xi and other party leaders.