Thousands of pro-democracy protesters have returned to the streets of Hong Kong in the first large-scale rally since demonstrations rocked the global financial hub late last year.

Some 2,000 police flanked an estimated 12,000 protesters marching on the city's glitzy shopping and financial districts, seeking to avoid a repeat of the so-called Occupy Central campaign that saw demonstrations shut down key roads for 2-1/2 months.

Last year's protests for a fully democratic vote to choose Hong Kong's next leader were the most serious challenge to China's authority since the 1989 pro-democracy demonstrations and crackdown in Beijing's Tiananmen Square.

While organisers stood fast to earlier demands for full democracy in the former British colony, they insisted the march would be peaceful and not seek to occupy any sites.

"We want to make it clear to the government that ... we want true universal suffrage," said Daisy Chan, one of the organisers.

Packed streets resembled rivers of yellow as protesters carried yellow banners and umbrellas - a symbol of last year's campaign after protesters used them to fend off police pepper spray attacks.

Chants of "we want true democracy" echoed off high rise buildings.

While the turnout by late afternoon fell far short of the 50,000 anticipated by organisers, some participants said they were pleased the spirit of last year's action had not been lost.

While anti-democracy groups were seen on the fringes of the protest, no scuffles were reported and police separated potential troublemakers.

Other protesters feared they might face violence from anti-democracy groups later in the evening, and some were arming themselves with protective shields.

Colonial-era Hong Kong flags and Union Jacks were seen flying among the crowds, prompting one old woman to yell at a student waving the British flag: "You say you want independence, but you don't."

The student, Sherman Ying, 20, said the protesters wanted their fates to be "controlled by us, not some government officials in Beijing or some puppet in Hong Kong".

"It is just that simple," he said.

Hong Kong returned to Chinese rule in 1997 and enjoys wide-ranging freedoms and autonomy under a so-called "one country two systems" arrangement but many fear tightening controls from Beijing.

Beijing has allowed city-wide elections for choosing the next chief executive in 2017, but wants to screen candidates first.

The prospect of screening has riled local democrats and their supporters, who fear pro-democracy candidates will effectively be barred from standing for election.