Tens of thousands of people have protested in Burkina Faso's capital, Ouagadougou, against moves to extend the president's 27-year rule.
Security forces fired tear gas to disperse protesters who hurled stones and burnt tyres, news agencies report.
Schools, universities and shops are shut for the week of planned protests.
It is one of the biggest protests demanding that President Blaise Compaore step down when elections take place next year.
On Thursday, Burkina Faso's parliament will consider a constitutional amendment that will allow him to run for another five years.
Mr Compaore took power in a coup in 1987, and has won four elections since then.
The opposition has called for a campaign of civil disobedience to force him to quit next year.
Protesters marched through the capital with banners reading "Blaise Get Out!", "Blaise = Ebola" and "We must disinfect ourselves", in reference to the highly contagious virus that has killed thousands of people in other West African states.
Women took part in the demonstration bearing raised wooden spatulas - regarded as a symbol of defiance.
Organisers said up to a million people took part in the march, but Reuters news agency reported that they numbered in the tens of thousands.
The security forces charged demonstrators after they apparently ventured too close to the parliamentary building, AFP news agency reports.