A Hong Kong feng shui master accused of forging the will of late property tycoon Nina Wang on Thursday urged the court to halt the case on the grounds the evidence has been tampered with.

Bartender-turned-fortune teller Tony Chan was arrested and charged last year after he lost a high-profile case in which he claimed the estimated $13 billion estate of Wang -- once Asia's richest woman whom Chan said was his lover.

But on Thursday his lawyer Alan Hoo told a magistrates' court that key evidence, including the will and its draft, had been tampered with due to fingertip and DNA tests conducted on the documents.

"It is a completely different document now," Hoo told the court on the second day of a preliminary hearing as he argued for a permanent stay of the case, adding that it mean "a fair trial is no longer possible."

Prosecutors however said the merits of the case should be heard before the court decides on the stay application.

"All that has taken place in this case has been fair, appropriate and carried out in accordance with the requirement of ensuring that the defendant's trial is fair," government counsel David Perry said.

The preliminary hearing is scheduled to go on until May 25 to allow both parties to iron out technical details on the charges before the trial proper starts. No date has been fixed for actual trial.

Chan built a career advising clients including Wang on feng shui, an ancient Chinese belief system based on harnessing natural and spiritual energies.

He lost his case for a piece of Wang's estate in 2010 after a court ruled that a will in Chan's possession was a fake. It said the rightful heir to the fortune was the billionaire's charity, which is run by her siblings.

Known for her outlandish dress and thrifty nature, Wang died of cancer in April, 2007 aged 69, triggering a bitter and very public feud over her fortune.