Kuwaitis have been casting their votes for the second time this year, in elections for a new parliament amid growing unrest.
On the eve of the election, tens of thousands of protesters in Kuwait City called for a boycott over changes made to the voting rules last month.
Opposition MPs say the amendment manipulates the ballot in favour of pro-government candidates.
Kuwait has had months of confrontations between the opposition and government.
Polling stations in the affluent Rumaithiya district of the capital appeared busy on Saturday morning, despite the calls for a boycott, the BBC's Shaimaa Khalil reports from Kuwait City.
However, the AFP news agency reported a far thinner turnout at a polling station in Salwa, 15km (10 miles) south of Kuwait City.
The main opposition grievance is a 19 October decree ordered by the emir, Sheikh Sabah al-Sabah, whose family dominates Kuwait's government.
The crisis was sparked in June, when the Constitutional Court annulled parliamentary elections held in February, in which the Islamist-led opposition made significant gains. The court also reinstated the previous assembly, allied to the ruling family.
After months of protests, Kuwait's emir ordered the dissolution of that parliament and announced new elections.
The emir's decree last month cut the number of candidates a voter can elect from four to one, saying it would ensure a fairer representation of people in the parliament.
But critics of the amendment say it gives the government greater influence over the outcome of the ballot.
Opposition MPs say the changes breaches the Gulf state's constitution. As a result they decided not to participate in the election.
Friday's protesters were angry at what they say is a unilateral decision by the emir to skew the election, which will not create a parliament representing the people, our correspondent reports.
This level of political polarisation is unusual in Kuwait, which has traditionally had a more unified political scene, she adds.
Carrying banners reading "absolute power corrupts", demonstrators marched through Kuwait City chanting, "we are boycotting" and "the people want to bring down the decree".
The rally was led by former Islamist MPs, by liberals and by young people, our correspondent says, adding that the mood was jubilant but defiant.
Unlike recent unauthorised protests, which ended in clashes between protesters and police, authorities had issued a permit for Friday's peaceful march.
Former MP Falah Al Sawagh told our correspondent the rally was not just about an electoral law, but about a long-term plan for real reform in Kuwait. "This is just the beginning," he said.
Demonstrator Rana Abdel Razak said the march would continue even after the election was held.
"We want real democracy, having elections doesn't mean we have democracy," she added.
Kuwait's parliament has the most powers of any elected body in the Gulf and opposition MPs openly criticise the ruling Sabah family.
However, the Sabahs retain full control over key government and executive posts.
The emir has dissolved parliament four times since 2006.