BEIJING, April 30 (Xinhua) -- A Chinese Ministry of National Defense spokesperson on Thursday voiced firm opposition to the United States and Australia strengthening their military presence in the South China Sea.

Spokesperson Wu Qian made the remarks at a press conference when asked to comment on reports about frequent U.S. military activities in the sea and airspace around China, U.S. warships and planes' multi-day training and their military exercise together with Australian navy in the South China Sea.

China is paying close attention to the movement of U.S. and Australian armed forces and remains on high alert, Wu said.

For a period of time, some countries outside the region, such as the United States and Australia, have frequently carried out military activities and strengthened their military presence in the South China Sea, he noted.

"This is not conducive to the security and stability of the South China Sea and we firmly object to it," Wu said.

Facts have proven time and again that the United States is the biggest driver of the militarization in the South China Sea and the troublemaker of regional peace and stability, he said.

The Chinese People's Liberation Army remains on high alert to resolutely safeguard China’s sovereignty, security, and development interests as well as regional peace, stability and prosperity, the spokesperson said.