Alpha Conde is a former opposition figure who in 2010 became the West African state's first democratically-elected president
Police deployed in large numbers Monday in the Guinean capital Conakry to break up protests against any changes to the constitution enabling 81-year-old President Alpha Conde to stay in power, an AFP reporter saw.
In the district of Cosa, an opposition stronghold, police fired stun grenades and teargas against groups of protesters.
An alliance of unions, opposition parties and civil society groups called the National Front for the Defence of the Constitution (FNDC) had appealed for a massive turnout.
Conde is a former opposition figure who in 2010 became the West African state's first democratically-elected president, but his tenure has been marred by a crackdown on protests.
Last month he called on the public to prepare for a referendum and elections, stirring speculation that he is planning to overcome a constitutional bar on a third term. The next presidential ballot is due to be held late next year.
The opposition says about 100 people have been killed since Conde took office in 2010, winning re-election five years later.
About 20 people have been arrested since Saturday, according to the FNDC.