The warning follows a report from US network CNBC last week that China had installed anti-ship and surface-to-air missiles on the Spratly Islands, an archipelago in the resource-rich waterway also claimed by Vietnam.

Hanoi called the latest moves a threat to peace and asserted Vietnam's historical and legal rights to the islands, which it calls the Truong Sa islands.

"Vietnam requests China... not to militarise (and) withdraw military equipment that were illegally deployed on structures under Vietnam's sovereignty," foreign ministry spokeswoman Le Thi Thu Hang said in a statement late Tuesday.

Vietnam and China have long sparred over who owns what in the South China Sea, which is believed to hold oil and gas deposits.

Tensions reached a fever pitch in 2014 when China moved an oil rig into waters claimed by Hanoi.

That sparked violent protests in Vietnam, though much of the wrangling between the communist neighbours over the disputed waterway has taken place behind closed doors since then.

The Philippines, Taiwan, Malaysia and Brunei also have also claims in the sea, but Vietnam has remained the most vocal opponent to Beijing's build up in the waterway.

Beijing hit back after Hanoi's demand to remove the missiles, with foreign ministry spokesman Geng Shuang telling reporters Wednesday, China has "indisputable sovereignty" over the islands -- which it calls the Nansha islands -- and surrounding waters.

Washington last week warned Beijing of unspecified "consequences" over its militarisation of the disputed waterway.