Citing a decision by the council of ministers, the the Ethiopian Broadcasting Corporation said: "A state of emergency has been declared as of now."
It gave no timeline for the emergency decree, the second since 2016, which was announced in a statement read by an anchor on the state broadcaster.
The communique eluded to "ethnic-based clashes" and "chaos and unruliness" as justification for the move.
"In some parts of the country, the constitution and the constitutional system has been bypassed," it said.
"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," it added.
"To be able to protect the constitutional system, declaring a state of emergency has become necessary."
The 10-month decree succeeded in quelling the unrest, which killed hundreds and resulted in tens of thousands of arrests, despite criticism from rights groups.
But anti-government sentiment remained in the two regions and protests continued to erupt sporadically.
The government was further pressured when clashes erupted late last year between the Oromo and Somali ethnicities that would go on to kill hundreds and, per a United Nations estimate, displace one million people.
Last month, Prime Minister Hailemariam Desalegn announced Ethiopia would begin releasing some jailed "politicians."
The move, he said, sought to "improve the national consensus and widen the democratic platform".
Tensions boiled over earlier this week when businesses closed and young men armed with rocks and sticks blocked roads in Oromia in a two-day strike to push the government to keep its prisoner amnesty promise.
The strike was called off after detained Oromo politicians were freed along with hundreds of other prisoners including journalist Eskinder Nega and opposition leader Andualem Arage.
The next day, Hailemariam unexpectedly announced he was stepping down, becoming the first leader in modern Ethiopia to do so.
The prime minister said he was leaving to give the ruling Ethiopian People's Revolutionary Democratic Front space as it pursued political reforms.
"I myself want to become part of the solution," he said.
But analysts say his departure was likely caused in part by his inability to unite the four ethnically based parties that constitute the coalition, which has been in power since 1991.
A member of the Wolayta ethnic minority in the country's south, Hailemariam was seen as lacking the charisma of his predecessor Meles Zenawi, who led the EPRDF to victory over the Derg communist Junta.
Hailemariam will remain in office until parliament and the EPRDF coalition confirm his resignation. It remains unclear who will then take over.
With the EPRDF and its allies controlling every seat in parliament, it is unclear what difference Hailemariam's departure will make, Merera Gudina, chairman of the opposition Oromo Federalist Congress, told AFP.
"What the people are demanding is fundamental change," Merera said, describing Hailemariam's exit as a matter of internal party politics. "So the change of an individual is really the homework for the EPRDF, not the people of Ethiopia."
However, Merera said he was "cautiously optimistic," that Hailemariam's departure could offer an opening for them.
"There are, after all, possibilities... to move forward," Merera said. "The EPRDF as an organisation has a serious problem and really blocked the democratisation of the Ethiopian state and society -- and is really responsible for many of its crisis," he added. (AFP)