By Louisa Lim BBC News, Beijing

Both Taiwan and China have increased their military power

Saturday's rally is to protest against a new Chinese law which would authorise the use of force against Taiwan if the island pushed for formal statehood.

China sees Taiwan as a breakaway province, and this bill gives it a legal basis to attack the island if it declares independence.

The march organisers are hoping to get a million people onto the streets.

Taiwan's President Chen Shui-bian has said he will join the march, which he has tried to paint as a peaceful rally aimed at protecting the island's democracy.

TAIWAN-CHINA RELATIONS Ruled by separate governments since end of Chinese civil war in 1949 China considers the island part of its territory China has offered a "one country, two systems" solution, like Hong Kong Most people in Taiwan support status quo Warning to Taiwan Taiwan Flashpoint

But China's state-run media is warning that the protests could worsen already tense relations between the two sides.

It quotes academics, who are often used as government mouthpieces, expressing fears that secessionist forces might use the march to fan anti-mainland sentiment.

China has tried to play down its new law, saying it is not a war bill.

But the law has drawn angry protests in Taiwan, where the government described it as a blank cheque for an attack on the island.

The new bill has also been criticised by the US, and has increased pressure on the European Union not to lift its arms embargo on China given the rising tensions across the Taiwan Strait.