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 which 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 said 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. But Taiwan sees itself as distinct from the Chinese mainland, with its own constitution and democratically elected leaders.

Tensions in the South China Sea flare up occasionally - most recently over the weekend, when ships from China and the Philippines figured in another encounter.

Manila accused a Chinese ship of deliberately ramming and firing its water cannon at a Philippine government vessel.

But Beijing said the incident happened after the Philippine vessel ignored repeated warnings and "dangerously approached" the Chinese ship.

The Philippines and Vietnam are also particularly sensitive to depictions of the South China Sea in maps.

The Barbie movie from 2023 was banned in Vietnam and censored in the Philippines for showing a South China Sea map with the nine-dash line.

The statement from China Customs did not say where the seized maps were intended to be sold. China supplies much of the world's goods, from Christmas lights to stationery.

The confiscation of "problematic maps" by Chinese customs officers is not uncommon, though the number of maps seized in Shandong easily eclipses past seizures. Goods that fail inspection at customs are destroyed.

In March, customs officers at an airport in Qingdao seized a batch of 143 nautical charts that contained "obvious errors" in the national borders.

In August, customs officers in Hebei province seized two "problematic maps" that, among other things, contained a "misdrawing" of the Tibetan border.