HONG KONG — Anti-Japanese protests spread across China over the weekend, and the landing of Japanese activists on a disputed island on Sunday sharply intensified tensions between the two countries.

Protesters took to the streets in nearly a dozen Chinese cities on Saturday and Sunday in response to Japan’s detention on Wednesday and deportation on Friday of a separate group of activists from Hong Kong, Macau and China who had landed on the same island, part of a chain of uninhabited islands known as the Diaoyu in China and the Senkakus in Japan. Demonstrations took place in cities up and down China’s eastern provinces, according to Xinhua, the official news agency.

The Chinese state news media portrayed the demonstrations as fairly small, each involving fewer than 200 people, and not extending to inland provinces. But photographs posted on Sina Weibo, the country’s most widely used microblogging service, suggested that the crowds had been far larger. In one photo said to be from the southwestern city of Chengdu, deep in China’s interior, the number of protesters appeared to be in the thousands.

“Defend the Diaoyu Islands to the death,” one banner said. Another said, “Even if China is covered with graves, we must kill all Japanese.”

Another photograph showed a handwritten sign taped to the entrance of Suning, a popular electronics store, telling customers it was no longer selling Japanese products.

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