A blockbuster corruption trial involving Hong Kong property tycoons Thomas and Raymond Kwok got under way Thursday, with all five defendants pleading not guilty to bribery charges.

The billionaire Kwok brothers, who jointly chair development giant Sun Hung Kai Properties, were arrested along with Hong Kong's former chief secretary Rafael Hui in a major swoop by the city's anti-graft watchdog in March 2012.

The Kwoks, aged 62 and 60, were accused of bribing Hui, who once held the second-highest position in the southern Chinese territory's government.

The trio are among five people charged with offences related to payments and unsecured loans amounting to HK$34 million (RM14.19 million).

The Kwoks are ranked fourth on the Forbes Hong Kong 2014 rich list, with an estimated family wealth of US$17.5 billion (RM56.1 billion).

Dressed in dark suits, the brothers smiled as they arrived at court in a storm of camera flashes, while more than 100 reporters waited inside.

Hui, 66, declined to discuss the case as he waited outside the courtroom, but told reporters he was "not feeling relaxed".

All the defendants, who have previously proclaimed their innocence, confirmed their not guilty pleas as the hearing got under way, with Thomas Kwok seen listening to a translation of proceedings through headphones.

Tight reporting restrictions were in place, with judge Andrew Macrae warning media to confine their coverage to the basic facts of the trial, following defence lawyers' criticism of earlier reporting.

Hui is accused of misconduct in being "favourably disposed to Sun Hung Kai Properties... and Thomas Kwok and Raymond Kwok" while in office in return for payments, according to a Department of Justice indictment.

The charges against Hui, who was the city's chief secretary from 2005 to 2007, also relate to rent-free use of luxury apartments and acceptance of unsecured loans, the document said.

The other defendants are another Sun Hung Kai director, Thomas Chan, and Francis Kwan, the former non-executive director of investment company New Environmental Energy Holdings.

After he was charged in July 2012, Raymond Kwok said: "I believe I have not done anything wrong and that the Hong Kong judiciary system is fair. I will fight the accusations and I hope it will prove my innocence."

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 iconic real estate including its tallest tower, the 118-floor International Commerce Centre.

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

But previous cases have fuelled public suspicions over cosy links between authorities and industry leaders, and the role of the Chinese system of personal connections, or "guanxi", which greases the wheels of business.

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 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.

The Kwok trial, which is expected to last 70 days at the city's High Court, will see a cast of prominent British lawyers in action.

Clare Montgomery, who represented the Swedish government when it requested the extradition of WikiLeaks founder Julian Assange from Britain, is representing Thomas Kwok, the elder brother.

John Kelsey-Fry, who successfully defended British footballer Steven Gerrard during a court case over a bar brawl in 2009, will represent Raymond. Another London lawyer, Ian Winter, is to represent Thomas Chan.