The announcement by the maritime safety authority in the coastal province of Fujian coincided with a statement from their counterparts in Hainan province that the navy was ending a three-day exercise in the South China Sea one day early.
While Beijing responded mildly to US President Donald Trump's early outreach to Taiwan's independence-leaning government, recent developments have prompted a tougher response. China claims Taiwan, which separated from the mainland during the Chinese civil war in 1949, as its own territory and says the sides must eventually be united, by force if necessary.
Chinese officials have denounced the recent passage of a US law encouraging more high-level contacts with Taiwan. China says the Taiwan Travel Act violates US commitments not to restore formal exchanges severed when Washington switched diplomatic recognition from Taipei to Beijing in 1979.
Beijing's Taiwan Affairs Office on Wednesday warned against additional moves to strengthen relations with Taiwan.
"Any attempt to play the 'Taiwan card' would only be futile," spokesman Ma Xiaoguang said. China, Ma said, would "not hesitate to protect our core interests."
That came after President Xi Jinping last month delivered a strongly nationalistic speech in which he vowed to protect "every inch" of China's territory.
China has also stepped-up air force missions in airspace around Taiwan and has repeatedly sailed its sole operating aircraft carrier, the Liaoning, through the 160 kilometer-wide Taiwan Strait.