Full coverage: The South China Sea Issue

China established Sansha City four years ago to strengthen its maritime law enforcement. The city plays a strategic role in the exercise of China's sovereignty in the South China Sea. Our reporter Han Bin returned to the city to look at how China is upgrading maritime law enforcement through joint efforts in promoting political structure, developing industries, and perfecting the legal system.

For maritime law enforcement, especially in disputed waters, you need to have some big ships.

But patrolling alone isn't enough.

This is Sansha's largest law enforcement vessel.

Captain Xiang Guoxiang showed us its functions.

He says the civil law enforcement vessels have close links with the coast guard and militia.

They have expelled foreign fishing vessels in waters claimed by China.

"The most effective means of law enforcement is the frequent patrols that push illegal foreign fishing boats away. We can feel the significance of our mission," said captain Xiang Guoxiang, No.1 Law Enforcement Vessel.

Some islands can only be reached by boat.

We're heading for Jinqing Island, the headquarters of the Yongle Island Group in Xisha.

Transportation is still the weakest link between islands in the South China Sea, making law enforcement very difficult.

Sansha has a three-tier law enforcement mechanism. The militia to find and report foreign infringement, civil law enforcement patrols, and coast guard support.

Fishermen agree that law enforcement is crucial.

"I have friends who had been arrested and detained by the Philippine government while fishing. Without active law enforcement, foreign vessels will come here and push us away," said Yang Zhen, fisherman.

Yang Zhen says the government is helping them get a better life.

Xiao Jie spends most of his time visiting islands in his jurisdiction.

He is happy to see the changes.

He has found that plants on Jinqing are are getting greener, as a result of environmental protection policies.

"Law enforcement means a combination of efforts to improve basic infrastructure, protecting the islands' eco-system, and ensuring the basic needs of fishermen, as well as disaster management, and search and rescue," said Sansha mayor Xiao Jie.

Xiao Jie believes effective law enforcement is one measure of the overall strength of Sansha's capabilities.

And for China's southernmost city, it's not all plain sailing.