The spotlight is on the district elections to gauge whether support for the democracy movement can translate into votes and bring change to the political landscape.
Hong Kong is semi-autonomous after being handed back by Britain to China in 1997, but there are fears that Beijing's influence is growing.
Tens of thousands of protesters took to the streets for more than two months at the end of last year demanding fully free elections for the city's next leader, in what became known as the "Umbrella Movement".
Some voters said the democracy movement had motivated them to cast their ballot.
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"It's the little power we have," said 28-year-old administrator Kris Fong, voting in the northern district of Yuen Long.
Fong said she had chosen a pro-democracy candidate because she felt the city was being "manipulated" by Beijing. She had missed previous elections but said voting this year was more important.
"After last year's umbrella revolution I feel that, however insignificant our vote might be, it's our only legitimate way to tell the people... Up north what we are thinking," said Fong, referring to powers in Beijing.
"I finally cast the first vote of my life," he said in a Tweet.
"Feeling exhilarated."
Just over 3.1 million residents are registered, with a 30 percent turnout by early evening.
The figure was slightly higher than at the same stage four years ago. Turnout at the end of the 2011 vote totalled 41 percent.
Polls close at 10:30 PM (2000 IST) and results are expected in the early hours of the morning.
Despite galvanising widespread support at the beginning of the mass street protests, democracy activists were unable to win concessions on political reform from the authorities in China or Hong Kong.