BEIJING — The reappearance on Saturday of Xi Jinping, a top Chinese leader who had vanished from public view, removes one question mark facing the Communist Party, but a wave of protests against Japan is a sign that internal power struggles are far from over.

On Saturday, the diplomatic tensions boiled over, with hundreds of demonstrators throwing rocks and eggs at the Japanese Embassy in Beijing, while smaller protests erupted in up to 40 other Chinese cities. Unconfirmed reports said some of the protests turned violent, with protesters said to have burned down a Toyota dealership.

Demonstrators were demanding that Japan give China control of a small group of islands known as the Diaoyu in China and the Senkaku in Japan.

Both countries claim them as part of their territory, but Japan exercises control over them.

Because any public gatherings are tightly controlled in China, it seemed likely that at least one faction in the government approved of Saturday’s protests. Protesters near the embassy in Beijing carried Chinese flags and pictures of the founding Communist leader Mao Zedong.