China claims the self-ruled island of Taiwan as part of its territory and has said it will not renounce using force to bring it under its control.

Beijing also claims almost the entire South China Sea, despite an international ruling that its assertion has no legal basis.

The maps were seized during an inspection of a batch of export goods in the eastern province of Shandong, customs authorities said in a statement on the messaging app WeChat.

The statement did not specify when the maps were confiscated or where they had been printed.

It said some of the maps mislabelled Taiwan and omitted “important” islands as well as the “nine-dash line”, which China uses to justify its maritime claims in the South China Sea.

Other maps seized did not contain the boundary line between the maritime islands of China and Japan.

These maps “endanger national unity, sovereignty, and territorial integrity” and are prohibited from being imported or exported, customs authorities said.

Maps have long been a sensitive topic for China and other countries in the region due to competing territorial claims.

Vietnamese police investigated in March Chinese tea brand Chagee over an online map featuring Beijing’s “nine-dash line”.

That same month Chinese-made “Baby Three dolls” were pulled from shops in Vietnam over a facial mark supposedly resembling the “nine-dash line”.