China's ambassador to Britain warned Wednesday of "chaos" in Hong Kong if pro-democracy campaigners go ahead with a plan to occupy the city centre and dismissed their calls for the public to nominate candidates in leadership elections.

Discontent in Hong Kong is at its highest level in years over what is seen as increasing interference from China and Beijing's insistence that it vet candidates before the vote for the city's next chief executive in 2017.

Pro-democracy group Occupy Central has vowed to take over the central business district if the government does not allow electoral reform.

"If unsatisfied, they threaten to 'Occupy Central' and bring the Hong Kong economy into chaos," Liu Xiaoming wrote in a comment piece in the Financial Times, published Wednesday, in the latest push back against the pro-democracy movement by Beijing.

"Any attempt to destabilise Hong Kong through street politics will certainly not win the hearts and minds of Hong Kong's people.

"Recent developments in some countries manifest one simple truth: street politics will not bring democracy but incur turmoil and chaos."

Beijing's state-run media has called Occupy "illegal" and said it could damage the city's economy.

An informal democracy referendum in Hong Kong last month, which drew a massive turnout of almost 800,000 people, also angered Beijing.

It was followed by a major pro-democracy march on July 1 which organisers said was the biggest protest since the city was handed back to China by Britain in 1997.

Beijing has promised to let all Hong Kong residents vote for their next leader in 2017 -- currently a 1,200-strong pro-Beijing committee chooses the city's chief executive.

But it says candidates must be approved by a nomination committee, which democracy advocates fear will mean only pro-Beijing figures are allowed to stand.

Activists have called for the vote to be conducted according to international standards, but Liu countered that.

"Electoral systems vary so, obviously, there is no 'international standard' to speak of," he wrote.

He likened the patriotism which Beijing has said is required of any chief executive to the oath of office taken by United States presidents.

Concerns over Beijing's influence increased in June when it published a controversial "white paper" on Hong Kong's future that was widely seen as a warning to the city not to overstep its bounds.

The white paper also said that loving China was a "basic political requirement" for any future leader.

Hong Kong enjoys liberties not seen on the mainland, including free speech and the right to protest, but there are growing fears that those freedoms are being eroded.