The decision caps a tumultuous week in Addis Ababa.
Ethiopia on Friday declared a state of emergency one day after Prime Minister Hailemariam Desalegn announced his resignation, state media reported.
"A state of emergency has been declared as of now," the Ethiopian Broadcasting Corporation (EBC) said, citing a decision by the council of ministers.
A statement read by an anchor on the state mouthpiece gave no timeline for the decree, the country's second since 2016.
The decision capped a tumultuous week in which some of Ethiopia's most prominent dissidents left jail in a prisoner amnesty, and anti-government protests rocked the country's largest region, Oromia.
"Because of the dangers the constitution and the constitutional system is facing, we have reached the point where it is difficult to keep the law in the usual way," according to the statement on EBC.
"To be able to protect the constitutional system, declaring a state of emergency has become necessary," the statement added.
Ethiopia last declared a state of emergency in October 2016 after months of protests in Oromia — home to the country's largest ethnicity the Oromos, and neighbouring Amhara region.
The 10-month decree succeeded in quelling the unrest, which killed hundreds and resulted in tens of thousands of arrests, but anti-government sentiment remains strong among both peoples.
Earlier this week businesses closed and young men armed with rocks and sticks blocked roads in Oromia in a two-day strike to push the government to release more prisoners.