The expansion is planned to protect China's maritime lifelines and its growing interests overseas, Hong-Kong based South China Morning Post reported today.
Some members would be stationed at ports China operates in Djibouti and Gwadar in southwest Pakistan, Chinese military insiders and experts were quoted as saying.
Gwadar port is a deep-sea port next to the Strait of Hormuz, the key oil route in and out of the Persian Gulf, built with Chinese funding and operated by mainland firms.
Gwadar also connects the USD 46 billion China-Pakistan Economic Corridor (CPEC) through PoK with China's Xinjiang.
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Reports from Pakistan said the country itself is setting up Special Security Division comprising 15,000 troops, including 9,000 Pakistan Army soldiers and 6,000 para-military forces personnel to protect CPEC and Chinese personnel.
The expanded Chinese marine corps is part of a wider push to refocus the world's largest army away from winning a land war based on sheer numbers and towards meeting a range of security scenarios using highly specialised units, the report said.
For this, two brigades of special combat soldiers had already been moved to the marines, nearly doubling its size to 20,000, and more brigades would be added, the report said.
"The PLA marines will be increased to 100,000, consisting of six brigades in the coming future to fulfil new missions of our country," it quoted a source as saying.
The size of the navy would also grow 15 per cent from its current estimated size of 2.35 lakh personnel.
Traditionally, marines have mostly operated only in China's coastal areas, as their role was limited by their relatively small numbers and basic equipment, Beijing-based naval expert Li Jie said.
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"Besides its original missions of a possible war with Taiwan, maritime defence in the East and South China seas, it's also foreseeable that the PLA Navy's mission will expand overseas, including protection of China's national security in the Korean peninsula, the country's maritime lifelines, as well as offshore supply deports like in Djibouti and Gwadar port in Pakistan," Li said.
China is constructing a naval base in Djibouti to provide what it calls logistical support in one of the world's busiest waterways in the Indian Ocean.
China denies it is an overseas military base but a logistics centre which will be used mostly for resupply purposes for anti-piracy, humanitarian and peacekeeping operations.
Liu Xiaojiang, a former navy political commissar, said the maritime force would take on an increasingly central role in the military.
"China is a maritime country and as we defend our maritime rights and develop our interests, the status of the navy will be more important," Liu told reporters on the sidelines of China's parliament session.
The plan calls for new trade and investment links stretching from Southeast Asia to eastern Europe, and will likely see Chinese companies as well as their workers operating in high-risk areas such as Pakistan and Afghanistan.
The marines were established in the 1950s in the aftermath of the civil war between China's Communists and Chiang Kai-shek's Nationalists who fled to Taiwan.
For decades, Taiwan had the second-largest marine force in the world, after the United States, but its stature began to decline in the 1990s when Beijing began pursuing claims in the South China Sea.