China's Defence Minister has urged preparations for a "people's war at sea" to counter offshore security threats and safeguard sovereignty, state media reported Tuesday.

Chang Wanquan's comments came several weeks after an international tribunal dismissed the country's claim to most of the South China Sea, a judgement it angrily rejected.

Chang "called for recognition of the seriousness of the national security situation, especially the threat from the sea", Xinhua news agency said.

The military, police and people should prepare to mobilise to defend national sovereignty and territorial integrity, he was quoted as saying during a tour of the coastal province of Zhejiang.

The agency did not say what day he was speaking or elaborate further.

Several Asian states have counter-claims in the South China Sea, where China has reclaimed reefs and islets to build airstrips and other major facilities.

The United States says it will continue naval patrols close to the reefs and outcrops to assert the principle of freedom of navigation, a move which has angered Beijing.

Ealier Tuesday China announced penalties for "illegal" fishing in its waters, including disputed areas.

The Supreme Court defined penalties for boats operating in "sovereign" areas including the South China Sea, in what appears to be an attempt to strengthen Chinese governance of the waters.

The question of who has the rights to fish in the disputed Sea has been a major bone of contention between Beijing and Manila, which brought the case to the Permanent Court of Arbitration in The Hague.

Beijing and Jakarta have also clashed over maritime rights, with Beijing claiming "historic" fishing grounds close to Indonesia's Natuna Islands.

The new regulations outline penalties for both Chinese and "foreign" fishermen operating "illegally" in Chinese waters, including its "exclusive economic zone" (EEZ), a 200-nautical mile region surrounding a country's territory.

The UN-backed tribunal denied China's claims to an EEZ in the Spratly Islands, where the Chinese coastguard regularly expels fishing vessels from the Philippines.

Beijing refused to accept the ruling, saying the court had no jurisdiction.

Those boats that "illegally enter" Chinese waters more than once in a year or refuse to leave the waters will be subject to fines and up to a year in jail, a posting on the court's website said.

It also established penalties for harvesting coral and giant clams, as well as other endangered species.

Any foreigners who believe that Beijing has violated their rights are welcome to take their claims to Chinese courts, the ruling said.

China also has maritime disputes with a number of other countries, including Japan and Vietnam.

Beijing risks triggering unintended conflict with Asian rivals through its aggressive stance in maritime disputes, Japan warned Tuesday in an annual security assessment.