Thousands of anti-Japanese demonstrators mounted protests in cities across China on Sunday over disputed islands in the East China Sea, a day after an attempt to storm Tokyo's embassy in the capital. Beijing was infuriated last week when Japan announced it had bought the rocky outcrops and while Chinese authorities often quickly suppress demonstrations, many of Sunday's events took place with police escorting the marchers. There were reports of violence. Demonstrators in Shenzhen -- some holding a banner calling for a "bloodbath" in Tokyo -- clashed with riot police, who fired tear gas to disperse the crowd, Hong Kong broadcaster Cable TV showed. It also showed footage of more than 1,000 protesters burning Japanese flags in the nearby southern city of Guangzhou and storming a hotel next to the Japanese consulate. Japan's Prime Minister Yoshihiko Noda called on China to ensure the safety of Japanese citizens and businesses after widespread protests on Saturday saw attacks on individuals, establishments and Japanese-built cars. "This situation is a great disappointment and so we are protesting" to China, he told Fuji Television. The relationship between China and Japan, the world's second and third largest economies, is often strained by their historical rivalry even though they have significant business links. The row over the islands, which Tokyo administers and calls Senkaku while Beijing claims them and knows them as Diaoyu, has heightened in recent weeks. Six Chinese ships sailed into waters around the disputed archipelago Friday, with Beijing saying they were there for "law enforcement", prompting Tokyo to summon the Chinese ambassador to protest what it called a territorial incursion.