Hong Kong property tycoon Thomas Kwok and the government's former deputy leader Rafael Hui were found guilty of corruption Friday in a blockbuster trial that shocked a city known for clean governance.

Kwok's billionaire brother Raymond was cleared after a seven-month trial over payments of HK$34 million ($4.38 million) the prosecution said were made to Hui to be their "eyes and ears" in government.

But in a complex case, the other pair were convicted over a payment of HK$8.5 million made to Hui, dating from the months leading up to his 2005 appointment to the government's second-highest post.

Hui, the most senior official ever arrested for graft, was found guilty on five of eight charges against him. Thomas Kwok was convicted of one count of conspiracy to commit misconduct in public office and cleared on another two charges.

Hui, who prosecutors said enjoyed an extravagant standard of living that far outstripped his official salary, was also found guilty on charges relating to rent-free use of luxury apartments and acceptance of unsecured loans.

Thomas Kwok, 63 and Raymond, 61, jointly chair development giant Sun Hung Kai Properties and were arrested along with Hui in a major swoop by graft investigators two years ago.

Prosecutors said fat bribes were made to Hui, who was chief secretary from June 2005 to June 2007, through a series of complicated transactions involving middlemen.

Two of the middlemen, Sun Hung Kai director Thomas Chan and Francis Kwan -- the former non-executive director of investment firm New Environmental Energy Holdings -- were both found guilty on two counts in the trial.

Speaking outside court a stunned Raymond Kwok said: "I'm happy that I was found not guilty but at the same time I am unhappy that Thomas and (Thomas) Chan Kui-yuen were proved guilty of the other charges.

"We will continue to support their families.

"I have to thank my family for supporting me throughout these two years."

A devout Christian, he also gave thanks to God.

- 'Black eye' for Hong Kong -

The case has shocked Hong Kong, where Sun Hung Kai is the biggest property developer by market capitalisation and owns some of the city's most recognisable real estate including the 118-floor International Commerce Centre.

The two brothers are ranked 62 on the Forbes rich list and are worth an estimated $14.45 billion dollars.

"It's a big black eye for the integrity of Hong Kong," said Francis Lun, a financial analyst and CEO of Hong Kong-based Geo Securities.

"The last thing you would expect is corruption at the top," he told AFP, adding that the city has had a well established anti-graft body since the 1970s.

"I suspect this isn't an isolated case, there must be other big business eyeing into the government too."

Lun said he had believed justice had been served.

"Rafael Hui destroyed the clean image of government and we now know the top of the Hong Kong government is corrupt and corruptible," Lun said.

The trial came as resentment in the city grows over the perceived cosy relationship between the government and the business elite -- one of the themes of the pro-democracy movement which gripped Hong Kong in recent months.

The southern Chinese city is seen as relatively graft-free -- it was ranked the joint 15th cleanest country or territory in 2013 by global corruption watchdog Transparency International.

However, the case revived discussion on links between wealthy tycoons and officials in the Asian financial centre that have long raised public suspicion.

Former Hong Kong chief executive Donald Tsang ended his term in disgrace in June 2012 after admitting to accepting gifts from tycoons in the form of trips on luxury yachts and private jets.

And Hong Kong billionaire Joseph Lau was in March found guilty of bribing a former minister in the gambling enclave of Macau in an attempt to purchase a prime development site in the former Portuguese colony.

Kwok and Hui, who had been on bail, have been remanded in custody until Monday when the court will reconvene for further arguments before the sentence is handed down.

The charge they were both found guilty of carries a maximum penalty of seven years' imprisonment.