HONG KONG -- Two billionaire brothers and the former senior Hong Kong official they're accused of bribing have pleaded not guilty as their high profile corruption trial got underway on Thursday.

Property developers Thomas Kwok and Raymond Kwok were arrested by anti-corruption officers more than two years ago along with Rafael Hui and two others in the former British colony's biggest graft case in decades.

The Kwoks control Sun Hung Kai Properties, which built several of Hong Kong's tallest skyscrapers and is one of the world's biggest real estate developers by market value.

Forbes estimates the pair are worth a combined $12.6 billion, making them Hong Kong's fifth richest.

The case has drawn widespread attention in Hong Kong, where a number of corruption cases involving tycoons or government figures has stoked public anger and fuelled concerns about widening inequality and collusion between officials and billionaires in the Asian financial hub.

Reporters and spectators packed into the Court of First Instance watched as the brothers made their pleas from the glass-walled dock, an unusual sight for Hong Kongers more accustomed to seeing the city's tycoons in luxurious settings.

Prosecutors allege the Kwoks bribed Hui while he was serving as Hong Kong's No. 2 government official. He's is the most senior Hong Kong official ever to be arrested.

They say he received payments and unsecured loans totalling about 34 million Hong Kong dollars ($4.4 million). They also say Hui received the use of apartments rent-free while he was head of Hong Kong's pension fund authority.

Hui faces eight counts including misconduct in public office, bribery and providing false information. Raymond Kwok faces four charges and Thomas Kwok faces three counts.