TEHRAN, Young Journalists Club (YJC) - Abiy took to national television in the early hours dressed in military fatigues and announced that army chief Seare Mekonnen had been shot, an AFP correspondent said. His condition was unknown.
The internet was cut nationwide in Ethiopia, and more details were not immediately available.
The United States embassy issued alerts about reported gunfire in the capital Addis Ababa, and violence around Amhara's main city Bahir Dar.
"The embassy is aware of reports of gunfire in Addis Ababa. Chief of mission personnel are advised to shelter in place," the embassy said in one of its two alerts.
Earlier, Abiy's office announced that an attempted coup had taken place in Amhara, the second-largest of nine autonomous regions which takes up much of the north of the country, and borders Sudan.
A statement from his office did not give details on who was believed responsible for the attack, the latest blow to his efforts to stabilise and reform the Horn of Africa nation.
"The coup attempt in Amhara regional state is against the constitution and is intended to scupper the hard won peace of the region," said the statement.
"This illegal attempt should be condemned by all Ethiopians and the federal government has full capacity to overpower this armed group."
No details were given of the targets of the attack in the second-most populous state in the country, headed by regional president Ambachew Mekonen.
A journalist in the regional capital Bahir Dar told AFP shooting had begun shortly after sunset and continued for several hours before ceasing.