Protesters in Senegal are angry about potential changes to electoral rules, fearing it will block many candidates from running in next year's presidential election.
The opposition says the proposals are a blow to democracy.
But the government insists the reforms are needed to simplify the election process and reduce state costs and subsidies allocated for campaigns.
Ahead of the vote, the government is banning protests in the city centre. Police are out in full force, firing tear gas.
Several key figures from the opposition and civil society have been arrested.
Al Jazeera's Nicolas Haque reports from Dakar.