The Chinese amphibious forces consists of 12,000 naval infantry and two army divisions trained to undertake amphibious operations. This is not, in a Western sense, a "marine corps." In the West, the nature of China's amphibious forces has been misunderstood for decades. Until the 1980s, the Chinese didn't have a marine corps, only army units that were trained to conduct amphibious operations. China didn't start building its own large amphibious ships until the 1980s, at the same time they organized marine brigades.
There are currently two Chinese marine brigades, containing a total of 10,000 troops, plus another 2,000 troops in support and training units. The marines are armed with amphibious armored vehicles and self-propelled artillery, anti-tank and anti-aircraft missiles. All of these marines are volunteers and undergo strenuous training. Each brigade also has a reconnaissance battalion, with several hundred men (and 30 women) trained to use scuba gear to get ashore and look around. These are actually special operations troops, and are carefully selected and trained. In Western terms, the Chinese marines are somewhere between the U.S. Marine Corps and the British Royal Marine Commandos in terms of training and intended capabilities.
Interestingly, the marines are not stationed where they could be used for an invasion of Taiwan, but in the south, where they can grab disputed islands. While these islands, which control fishing and potential oil fields, are considered disputed, China has already laid claim to some of them by force. In 1974, China fought a naval battle with Vietnam off the Paracel islands. In 1988, China and Vietnam fought another naval battle, off the Spratly islands. Both of these battles were followed by Chinese troops establishing garrisons on some of the islands. In 1992, Chinese marines landed on Da Lac reef, in the Spratly Islands. In 1995, Chinese marines occupied Mischief Reef, which was claimed by the Philippines.
The Chinese marines are trained and equipped for raiding, not for large scale landings against a defended shore. The latter task is apparently left to army divisions that have been drilled on how to get on, and off, amphibious ships. While the Chinese marines might play a part in a Taiwan invasion, their full time job appears to be in the South China Sea, where the Chinese stand ready to grab more islands, if the economic advantages seem high enough. The navy supplies the amphibious ships and any air support (fixed wing aircraft and helicopters) needed. Detachments of marines have accompanied the warships China sends to the anti-piracy patrol off Somalia.