Beijing has said Taiwan leader Chen Shui-bian is trying to ruin cross-Straits ties, as it reacted angrily to his New Year message insisting the island was not part of China, according to state media reports.

An unnamed spokesman from the Beijing's Taiwan Affairs Office also reiterated that China would never allow the island, separated from the mainland by the narrow Taiwan Strait, to formally break away, the People's Daily reported.

"Chen intends to unreasonably restrict cross-Strait exchanges and cooperation, worsen the atmosphere of cross-Strait relations, and ruin the peaceful and stable development of cross-Strait ties," he was quoted as saying.

"We will be highly vigilant to any secessionist moves and never allow secessionists to separate Taiwan from the motherland in any name or by any way," he said.

The mainland and Taiwan split in 1949 at the end of a civil war.

Taiwan's independence-leaning leader insisted Monday in a New Year's message that the island's sovereignty lay in its own hands.

"Hereby we must stress that Taiwan is our country. Taiwan's sovereignty belongs to 23 million people. It definitely does not belong to the People's Republic of China," Chen said after a flag-hoisting ceremony.

"Only the 23 million have the right to decide on the future of Taiwan. Taiwan is part of the world but not part of China," he said.

His remarks came after China issued a key defence paper arguing it needs a strong and credible military and citing security challenges it said it cannot ignore, such as Taiwan's independence drive.