A Chinese-Australian property developer has been helping Beijing build an extradition case for an allegedly corrupt billionaire hiding out in the United States, ahead of President Xi Jinping's visit to Washington this week.

Zheng Jiefu, who has been living in Melbourne for the past six years, told the Australian Financial Review he has been in close contact with the Communist Party's anti-corruption arm in recent months over his business dealings with Guo Wengui.