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 stated.

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

China Customs also reported that the maps did not include the nine-dash line, which demarcates Beijing's claim over nearly the entire South China Sea. The line extends hundreds of miles south and east from its most southerly province of Hainan.

The confiscation of 'problematic maps' by Chinese customs is not uncommon, though the scale of this seizure surpasses previous ones. In March, customs officers in Qingdao seized 143 nautical charts containing 'obvious errors' in national borders.

This incident adds to the ongoing tensions in the South China Sea, particularly illustrated by recent confrontations between Chinese and Philippine vessels.

The Philippines and Vietnam also show strong sensitivities about South China Sea depictions on maps; for instance, the Barbie movie was recently banned in Vietnam and censored in the Philippines over related content.