The number of Chinese maritime incursions near Japanese-held islands in the East China Sea soared to a record this year, illustrating simmering tensions between Asia’s two biggest economies.

Chinese government ships, including coast guard vessels, have entered what Japan considers its exclusive waters more than 1,000 times this year, according to data from the Japan Coast Guard. That’s on track for an 80 percent increase over last year, and far more than any year since 2012, when China began making regular incursions around the islands.

The patrols — along with the recent detention and release of a Japanese academic accused by China of stealing state secrets — show how key disputes between the two neighbors remain unresolved even as they publicly tout warming ties.

Prime Minister Shinzo Abe is expected to hold talks with Chinese President Xi Jinping during his planned visit to China later this month, Chinese Vice President Wang Qishan said Friday. It will be Abe’s second trip to China in little more than a year, and he is hoping to host Xi on a state visit next year.

The remark by Wang, a close aide to Xi, came during a meeting in Beijing with Shigeru Kitamura, a former top intelligence officer who has served as Abe’s national security adviser since September.

While it’s unclear what’s driving the uptick in maritime incursions, Beijing has long sought for Tokyo to formally acknowledge the dispute over the small, uninhabited islands, known as the Senkakus in Japan and the Diaoyus in China. A decision by Abe’s predecessor in 2012 to purchase some of the islands prompted a wave of anti-Japanese demonstrations and boycotts and led Beijing to step up maritime patrols.

The Chinese Ministry of Foreign Affairs in Beijing didn’t respond to a request for comment Thursday. China holds that the islands — located just north of Taiwan and surrounded by potential natural gas deposits — are part of its historical territory that should have been returned with the rest of Japan’s colonial possessions after World War II.

Abe has spent much of his seven-year tenure trying to repair ties with China while maintaining Tokyo’s postwar alliance with Washington. That effort has been tested in recent months by Japanese officials’ defense of peaceful protests in Hong Kong and Tokyo’s move to effectively exclude Huawei Technologies Co. from government contracts.

At least 14 Japanese citizens have been detained in China since 2015, according to Japan’s Foreign Ministry. Five have since been released while another nine remain in custody under accusations of violating national security laws.

The increased maritime patrols will make Abe’s balancing act more difficult during his visit to China, where he is also expected to hold a trilateral summit with Chinese Premier Li Keqiang and South Korean President Moon Jae-in.

Fisheries cooperatives in Okinawa Prefecture, where the islands are located, have complained about being forced away from waters due to Chinese patrols while right-wing politicians have encouraged Abe to take a hard line with China in the territorial dispute.

“China is engaging in unilateral and coercive attempts to change the status quo based on its own assertions incompatible with the existing international order, and has been expanding and intensifying its military activities in maritime and aerial domains,” the Japanese Defense Ministry said in annual policy paper published in September.