Chief Executive CY Leung and other government officials in his administration urged the public to come out to vote as polling stations opened at 7.30 a.m., and are due to close 15 hours later, the South China Morning Post reported.
The three main groups -- pro-Beijing parties including pro-business parties; traditional pro-democracy parties known as pan-democrats; localists who want democracy but think there should be more confrontation with the government -- competing are divided by their stances on the territory's relationship with Beijing, the BBC reported.
Leung said he believed voters would have their own "independent minds" when picking their candidate, as he and wife visited a polling station at 8.11 a.m. to cast their votes.
"Democracy is reflected in the freedom of choices of the voters. The electors can have their own choice. There is no need for other people to teach them how to vote," the South China Morning Post quoted the Chief Executive as saying.
The seats are in the Legislative Council, which passes laws and budgets in the territory.
Voters will choose 35 lawmakers based on geographical constituencies and 35 people to represent selected trades, the BBC said.
The city has partial democracy and not everybody can vote for all the seats.
Thirty seats are decided by a pool of just 6 per cent of just 239,724 people. Hong Kong has 3.7 million voters.
The vote does not elect the Chief Executive, who is the head of government, but many analysts believe the outcome of Sunday's vote could have an impact on whether China grants current leader CY Leung a second term in office, the BBC reported.
For two months in 2014 protesters demanded his resignation as the Occupy movement occupied major parts of the city and caused political upheaval while calling for the right to elect a leader directly.
