Chinese state media have hit out at US "trouble-making" on the South China Sea, two days after Beijing summoned a US diplomat on the issue.

One commentary told the US to "shut up" on the subject, while another said it had "deservedly evoked curses".

The response came after the US State Department said it was "closely" monitoring increased tensions in the South China Sea.

It also expressed concern over China's move to militarise a disputed island.

"In particular, China's upgrading of the administrative level of Sansha City and establishment of a new military garrison there covering disputed areas of the South China Sea run counter to collaborative diplomatic efforts to resolve differences and risk further escalating tensions in the region," acting deputy spokesman Patrick Ventrell said in a statement on Friday.

Sansha City lies on Woody Island in the Paracel Islands, which China has controlled since a battle in 1974 with Vietnam. Taiwan also claims the islands, whose population numbers only a few thousand, mostly fishermen.

The city was established in June as China's administrative base for the whole South China Sea area, including the disputed territories of the Spratly Islands and the Scarborough Shoal.