What is China violating in East Sea?

However, irrespective of its UNSC membership, China continues its assertiveness, flagrantly ignoring international law and carrying out aggressive acts in the East Sea.
As a result, tensions in the East Sea are continuing to escalate following China’s illegally stationing of its oil rig Haiyang Shiyou- 981 and deployment of dozens of ships, including military vessels in Vietnam’s exclusive economic zone and continental shelf.Chinese ships have many times attacked Vietnamese law enforcement forces and the international community has voiced its concern and opposition of China for its serious violation of international law and high-level agreements reached by Vietnam and China, which are adversely affecting peace and security in the region.

Leading experts report that it is not hard to prove that China's actions have violated the 1982 UN Convention on the Law of the Sea (UNCLOS), the UN Charter, the Declaration on the Conduct of Parties in the East Sea (DOC) and other relevant documents as well as trying to mislead the media.
Drilling rig position and UNCLOS
The position China has installed it drilling rig Ocean-981, 120 nautical miles from Tri Ton island belonging to Vietnam’s Hoang Sa (Paracel) archipelago shows that China has illegally occupied 17 nautical miles of Vietnam’s territorial waters.
According to Dr. Nguyen Thi Lan Anh (Vice Dean of the Diplomatic Academy of Vietnam’s International Law Department), the above-mentioned location is within deep in Vietnam’s exclusive economic zone and continental shelf.

Article 57 of the UNCLOS-1982 stipulates that the width of the exclusive economic zone of a coastal state will not exceed 200 nautical miles, and Article 76 of the Convention says that one of the options to define the width of the continental shelf of a coastal state is a minimum of 200 nautical miles. Another way to define the width bigger than 200 nautical miles is that if the real continental shelf is larger than 200 nautical miles, the coastal states may extend their continental shelf up to 350 nautical miles or not exceeding 100 nautical miles since the from 2,500 m depth contour line.
Pursuant to the boundary of 200 nautical miles, the location of the Chinese drilling oil is within deep in Vietnam’s continental shelf and exclusive economic zone, Lan Anh said.
A Chinese Foreign Ministry spokesperson said that this is China's Xisha waters and its placement of a drilling rig is a normal activity.

First of all, it is essential to clarify that China has used Xisha to name Vietnam’s Hoang Sa (Paracel) archipelago and Vietnam have sufficient legal evidence to affirm its sovereignty.
After the World War II, the UN Charter was issued with the aim of maintaining peace and stability in the world.  The Charter stipulates that peace and settlement of disputes is mandatory obligations for member state and member states are not allowed to threaten the use of force.
China has been a UN member but it has used force to illegally occupy Vietnam’s Hoang Sa (Paracel) islands when the UN Charter was in effect. This is a flagrant violation of the UN Charter. Therefore, it is impossible to establish a Chinese sovereignty in the Paracel islands.
China should ask for Vietnam’s permission to put the rig
Dr. Nguyen Thi Lan Anh affirmed that China has violated the fundamental principles, including Vietnam’s sovereign rights and jurisdiction under Article 56 and Article 76 of the UNCLOS.
China’s illegal installment of a drilling rig aiming to explore and exploit natural resources associated with the seabed of the continental shelf lies entirely in natural resources area belonging to sovereign rights of a coastal state that is Vietnam.
National jurisdiction in these waters is the licensing right to allow other countries to install or build floating works at sea. China’s oil rig Haiyang Shiyou- 981 is a floating work that it has placed in Vietnam’s continental shelf without the country’s permission. This means that China has violated Vietnam’s jurisdiction.
"The UNCLOS also states that all drilling and exploration activities on the continental shelves must get permission from coastal states. Vietnam has not yet allowed China to conduct such activities", Dr. Lan Anh emphasized.
Deputy Prime Minister cum Foreign Minister Pham Binh Minh reiterated that Vietnam has sufficient legal and historical foundations to affirm its sovereignty over Hoang Sa (Paracel), Truong Sa (Spratly) islands and sovereign rights and jurisdiction over exclusive economic zone and continental shelf in accordance with the UNCLOS.
Vietnam will take all appropriate measures to protect its legitimate rights and interests. At the same time, the country has always shown its goodwill and tenacity to satisfactorily resolve disputes through negotiations, dialogues and other peaceful means in line with the common perception of the two nations’ senior leaders and agreements on the fundamental principles on settlement of maritime issues in accordance with regulations and practices of international law, particularly the UNCLOS-1982 to avoid damaging political trust and cooperation between the two sides.