Sydney - A Democrat in the White House after next week's presidential election could usher in a round of protectionism that would do further damage to the world economy, media baron Rupert Murdoch warned Saturday.

The chairman and chief executive of US-based News Corp said imposing new tariffs on Chinese imports could be the blue touch paper for a trade war.

"For the past three or four years some Democrats have been threatening to do things like put on extra tariffs (against Chinese imports) if they don't change their currency," he told The Australian newspaper. "If it happened, it could set off retaliatory action which would certainly damage the world economy seriously."

Australian-born Murdoch, who is now a US citizen, said that if Senator Barack Obama won the presidency he could be pressured to implement protectionist measures.

"Presidents don't often behave exactly as the campaign might have suggested because they become prisoners of all sort of things - mainly circumstances and events," he said.

Murdoch labeled as "rubbish" Obama's plan to give tax rebates of 95 per cent of Americans. "Forty per cent don't pay taxes, so how can he give them a tax cut?" he said.

Murdoch said a rise in protectionism "could add to all sorts of tensions in the world financial system and the world trading system and eventually all the way down to employment."

He warned against believing it was in the power of governments to heal the financial system. "You are going to find that the politicians are very limited in what they can do: they can make it worse but they can't stop it." (dpa)