The scathing comments follow U.S. President-elect Donald Trump's telephone call with Taiwan's leader Tsai Ing-wen that deeply upset Beijing.
Quoting a poem by the founder of Communist China Mao Zedong, China's government said on Wednesday that the efforts by Hong Kong and Taiwan separatist supporters to link up were doomed to fail, as they would be "dashed" to the ground like "flies."
Chinese leaders are increasingly concerned about a fledgling separatist movement in the former British colony of Hong Kong, which returned to mainland rule in 1997 with a promise of autonomy, and recent protests in the city.
China is also deeply suspicious of Taiwan President Tsai Ing-wen, elected earlier this year, who Beijing suspects is pushing for the self-ruled island's "independence."
Beijing has already warned about independence activists in both places linking up — Hong Kong activists have visited Taiwan this year — and went further at a routine news conference by China's policy-making Taiwan Affairs Office.
"A small coterie of Taiwan independence forces are trying in vain to link up with Hong Kong independence (forces) to split the country, which cannot succeed," spokesman An Fengshan said.
"It's just like that saying 'On this tiny globe, a few flies dash themselves against the wall'," said An, quoting a 1963 poem by Mao, lines usually taken to mean that China does not fear its enemies.
"In the end they'll find themselves broken and bleeding," he added, without elaborating, using words that are not in the poem.
The comments come amid renewed tension over Taiwan, following U.S. President-elect Donald Trump's telephone call with Tsai that deeply upset Beijing.
China has never renounced the use of force to bring the island under its control after defeated right-wing nationalist forces fled there at the end of a civil war with the Communists in 1949.