China firmly opposes plans by the United States government to offer arms assistance to Taiwan and its sending of instructors to help train the military on the island, a Defense Ministry spokesman said, adding that it has made solemn representations to the US side.

Some media reported that the US government is planning to provide Taiwan with $500 million worth of arms assistance under what's known as a Presidential Drawdown Authority. Using a drawdown will let the US sidestep the often-lengthy process of contracting and producing weapons. Additionally, the US has recently sent instructors to Taiwan to assist in training soldiers there.

"For some time now, the US has continuously strengthened its military collusion with the Democratic Progressive Party authorities in Taiwan, elevating their military ties and upgrading substantive relations, which has shaken the foundation of China-US relations and undermined peace and stability across the Taiwan Strait," spokesman Tan Kefei said on Tuesday.

"This is a highly erroneous and dangerous move. We are strongly dissatisfied and firmly oppose it. We have made solemn representations to the US."

The Taiwan question is the core interest of China and an unbreakable red line for China-US relations, Tan said, noting that breaking diplomatic relations, abandoning the Mutual Defense Treaty and withdrawing troops are the premise for the establishment of China-US diplomatic relations and cannot be reversed by anyone.

"We warn the US side to earnestly abide by the one-China principle and the three Sino-US Joint Communiques, to follow through on their commitment of not supporting 'Taiwan independence', and to cease any form of military collusion with Taiwan," Tan said.

"We also warn the DPP authorities and 'Taiwan independence' separatist forces that any attempt to seek independence through collusion with the US or independence through military means is a dead end."

The Chinese People's Liberation Army will continue to strengthen their combat readiness and resolutely crush any form of "Taiwan independence" separatist activities and foreign interference, firmly safeguarding national sovereignty and territorial integrity, he added.

When commenting on bilateral security guidelines between the US and the Philippines, Tan said China firmly opposes any country interfering in the South China Sea issue and undermining China's territorial sovereignty and maritime rights and interests under the pretext of so-called bilateral treaties.

Under the guidelines, the US said it will come to the Philippines' defense if its armed forces came under attack anywhere in the South China Sea.

"Through the joint efforts of regional countries, the current situation in the South China Sea remains generally stable. The South China Sea should be a sea of peace, friendship and cooperation, rather than a battleground for certain countries to engage in camp confrontation," Tan said.

"China's position on the South China Sea issue has always been consistent and clear. The Chinese military closely monitors relevant developments and will take necessary measures to resolutely defend national territorial sovereignty and maritime rights and interests, and firmly maintain peace and stability in the South China Sea."