The protests came in response to increases of up to 120 percent in fuel prices after the government eliminated subsidies as part of an agreement with the International Monetary Fund (IMF) to obtain loans despite its high public debt.
The IMF agreement, signed in March, allowed Ecuador to borrow $4.2 billion.
Police fired tear gas at protesters who threw stones and firebombs close to the seat of government in the historic center of the capital Quito.
Moreno told reporters he had taken the emergency measure “to safeguard the security of citizens and to avoid chaos.”
The clashes paralyzed public transportation in some areas, while clashes between police and demonstrators blocked roads.
More than 21 police officers had been injured in the violence while 277 people had been arrested for “vandalism,” said defense minister Oswaldo Jarrin. No figures were available for the total number of people wounded but some press photographers were hurt during the clashes.
Moreno blames the deterioration in the country’s finances on his predecessor, Rafael Correa, who has sought asylum in Belgium.
The left-wing former president is wanted back home for allegedly kidnapping a political opponent in 2012 during his 10-year presidency. Correa adamantly rejects the charges, saying he is being persecuted. Interpol has refused Ecuador’s request to arrest him.
Moreno’s emergency measure allows the government to restrict movement, to employ the armed forces to maintain order and to censor the press. It will be in place for 60 days, after which it can be extended for a further 30 days, the government said.
School suspensions were extended into Friday, while buses and taxis stopped operating in Quito and other large cities.
Unions and indigenous organizations are also planning protests.
Moreno said he would not allow protesters to “impose chaos,” and also 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 – a turbulent period in which Ecuador had a total of seven holders of its highest office.
The scrapping of fuel subsidies is part of the broader IMF agreement that requires the government to make sweeping cuts the federal budget – equivalent to about 6 percent of GDP over the next three years. The program will force the government to lay off thousands of public employees.
Economist Mark Weisbrot of the U.S.-based Center for Economic and Policy Reseach warned in an August op-ed for the Guardian that the austerity program is likely to cause a recession and that the downturn will be “deeper and longer” than the IMF projects.
The Globe Post’s Bryan Bowman contributed reporting to this article.