LONDON (AFP) - WikiLeaks on Tuesday launched a crowdfunding campaign to raise a €100,000 (S$150,000) reward for anyone leaking insider information on a proposed free-trade deal between the United States and European Union.

The controversial whistleblowing website, which hit the headlines in 2010 after publishing more than 700,000 classified US government documents, had already reached 20 per cent of its target by Tuesday afternoon.

High-profile donors included Greece's former finance minister Yanis Varoufakis, fashion designer and environmental campaigner Vivienne Westwood, journalist Glenn Greenwald and WikiLeaks editor-in-chief Julian Assange.

Hundreds of demonstrations were held in April, mainly in Europe, against the Transatlantic Trade and Investment Partnership (TTIP).

"TTIP, which is currently under negotiation between the US and the European Union, remains closely guarded by negotiators and big corporations have been given privileged access," said a WikiLeaks statement. "The public cannot read it."

"Today, WikiLeaks is taking steps to ensure that Europeans can finally read the monster trade deal," it added.

"The secrecy of the TTIP casts a shadow on the future of European democracy," warned Assange.

"Under this cover, special interests are running wild. The TTIP affects the life of every European and draws Europe into long term conflict with Asia. The time for its secrecy to end is now."

Assange is currently holed up in London's Ecuadorian embassy where he is fighting extradition to Sweden for questioning over allegations of rape and sexual assault.

If concluded, TTIP would be the world's biggest trade deal, linking about 60 per cent of the globe's economic output in a colossal market of 850 million consumers, creating a free-trade corridor from Hawaii to Lithuania.