Protesters clashed with police after Ecuadoran President Lenin Moreno declared a state of emergency on Thursday, after rallies against rising fuel prices due to the government scrapping subsidies.
Police fired tear gas at protesters who threw stones and Molotov cocktails close to the seat of government in the historic centre of the capital Quito.
Mr Moreno said he had made the declaration to protect "the security of citizens and to avoid chaos".
The protests, which were the largest in a decade, were led by the transport sector but included students and other groups.
They stopped public transport in some areas, while clashes between police and demonstrators blocked roads.
Interior Minister Maria Paula Romo said 19 people have been arrested.
No figures were available for the number of people injured during the clashes.
The rallies came in response to increases of up to 120 per cent in fuel prices, which began on Thursday after the government scrapped subsidies as part of an agreement with the International Monetary Fund to obtain loans despite its high public debt.
A gallon of diesel rose from $1.03 (Dh3.78) to $2.30, while regular petrol increased from $1.85 to $2.40. The price of premium petrol was already increased a year ago.
The subsidies cost the government $1.3 billion a year. The IMF agreement, signed in March, allowed Ecuador to borrow $4.2bn.
Mr Moreno blames the deterioration in Ecuador's finances on his predecessor, Rafael Correa, who has sought asylum in Belgium.
Mr Correa is wanted back home on suspicion of kidnapping a political opponent in 2012 during his 10-year presidency.
The emergency measure allows the government to restrict movement, use the armed forces to maintain order and censor the press.
It will be in place for 60 days, after which it can be extended for another 30 days, the government said.
School classes were suspended on Thursday while buses and taxis stopped operating in Quito and other large cities.
Unions and indigenous organisations are also planning protests.
Mr Moreno called for an end to "acts of vandalism and acts of violence".
Between 1996 and 2007, mass street protests forced the resignation of three presidents. Ecuador had seven presidents in that time.