Chinese customs officers in eastern Shandong province have seized 60,000 maps that mislabelled the self-governed island of Taiwan, which Beijing claims as part of its territory.

The maps, authorities said, also omitted important islands in the South China Sea, where Beijing's claims overlap with those of its neighbours, including the Philippines and Vietnam.

The problematic maps, meant for export, cannot be sold because they endanger national unity, sovereignty and territorial integrity of China, authorities said.

Maps are a sensitive topic for China and its rivals for reefs, islands and outcrops in the South China Sea.

China Customs said that the maps also did not contain the nine-dash line, which demarcates Beijing's claim over nearly the entire South China Sea.

The line comprises nine dashes that extend hundreds of miles south and east from its most southerly province of Hainan.

The seized maps also did not mark the maritime boundary between China and Japan, authorities said.

Authorities stated that the maps mislabelled Taiwan province, without specifying what exactly the mislabelling was.

China sees self-ruled Taiwan as its territory and has not ruled out the use of force to take the island. In contrast, Taiwan views itself as distinct from the Chinese mainland, with its own constitution and democratically elected leaders.

Recent tensions in the South China Sea flared up, particularly when ships from China and the Philippines encountered each other. Manila accused a Chinese ship of deliberately ramming and firing its water cannon at a Philippine government vessel, while Beijing countered that the Philippine vessel ignored warnings.

The Philippines and Vietnam remain particularly sensitive to how the South China Sea is depicted in maps.

The statement from China Customs did not specify where the seized maps were intended for sale. China is a major supplier of goods worldwide, ranging from Christmas lights to stationery.

The confiscation of problematic maps by Chinese customs officers is not uncommon, yet the number of maps seized in Shandong surpasses previous operations. Any goods failing inspection at customs are typically destroyed.

This incident follows other recent seizures, including a batch of nautical charts in Qingdao that contained errors regarding national borders and two problematic maps seized in Hebei province which featured a misdrawing of the Tibetan border.