Beijing stepped up its rhetoric against Taiwanese independence on Saturday, with Premier Li Keqiang warning against "separatist activities" on the island and pledging to safeguard China's "territorial integrity".

Li's comments at the opening of the mainland's National People's Congress (NPC) parliament came weeks after Tsai Ing-wen, chairwoman of the Beijing-sceptic Democratic People's Party, was elected Taiwan's next president.

Beijing will "oppose separatist activities for the independence of Taiwan" and "safeguard China's sovereignty and territorial integrity", Li told the Communist-controlled legislature.

Both clauses were additions to the remarks he made on the issue at last year's NPC, when the Beijing-friendly Kuomintang of current leader Ma Ying-jeou was still hoping to retain power in Taipei.

China and Taiwan split in 1949 after a civil war but Beijing still considers the self-ruled island part of its territory awaiting reunification, and has an estimated 1,500 missiles aimed at stopping Taiwan from declaring independence.

Beijing has repeatedly asserted its belief in the "1992 consensus", which says that there is only "one China", despite allowing Taiwan to make its own interpretation.

But the DPP -- which does not recognise either the "one China" principle or the "consensus" -- triumphed in the island's January parliamentary and presidential elections as voters turned their backs on closer ties with the mainland.

Li Keqiang spoke Saturday of people on both sides of the Taiwan Strait as "fellow compatriots" belonging to "one and the same family" sharing a "common destiny".

The phrasing echoed President Xi Jinping's rhetoric from last November, when the leaders of China and Taiwan reached across decades of Cold War-era estrangement and rivalry to exchange a historic handshake in the first summit since the two sides split.

"We are brothers connected by flesh even if our bones are broken. We are a family whose blood is thicker than water," Xi said then.

Tsai will take office in May, and though she has radically toned down her party's traditionally pro-independence platform, analysts agree a deterioration of ties is inevitable.