The Chinese mainland is warning Taiwan authorities that "courting foreign support to build you up will only invite trouble", a spokesman for the mainland said on Wednesday.

"The Taiwan question concerns China's sovereignty, territorial integrity and the national feelings of the Chinese people," Ma Xiaoguang, spokesman for the State Council Taiwan Affairs Office, said at a news conference.

"We will never waver in safeguarding China's core interests," Ma said.

Asked about possible visits to Taiwan by officials from the United States and the US State Department's approval of a marketing license for sales of military submarine technology to Taiwan, Ma urged the US to abide by the one-China policy and the principles of the three Sino-US Joint Communiques.

Any outside forces that attempt to "play the Taiwan card" will find their efforts "futile" and will hurt themselves if they go "over the line", he said.

Asked about Taiwan's response to Sino-US trade disputes, Ma said a few people in Taiwan wanted to take advantage of the disputes to do things that were "not upright", and have lifted a stone that will "smash their own feet".

"Returning to the right track of the 1992 Consensus and the peaceful development of cross-Straits relations is the only way Taiwan can avoid becoming a pawn of others," he said.

Ma also hailed the benefits of cross-Straits economic cooperation, promising that a more open mainland would create new opportunities for compatriots and businesses in Taiwan.

He said that the mainland's policy to support Taiwan businesspeople coming to the mainland is coherent and clear, and that if the Taiwan business community seizes the opportunity, it will enjoy better development.

"Anyone who wants to hinder cross-Straits economic cooperation will fail," he said.

Ma reiterated that China strongly opposes the United States selling weapons to Taiwan.

"We firmly oppose any official or military connection between the US and Taiwan, and also object to any form of weapons sale to the island," he said in response to a question about a bill signed recently by US President Donald Trump that allows for direct contacts between US and Taiwan officials.

He added that the Taiwan question is about Chinese sovereignty and territorial integrity.

Earlier this week, the Ministry of National Defense announced its strong opposition to US weapons sales to Taiwan.

"China's military has the ability and resolve to defeat all attempts to separate our country, and it will adopt all necessary measures to resolutely defend national sovereignty, security and territorial integrity," ministry spokesman Wu Qian said.