Report by a spokesman for the regional authorities, Nigusu Tilahun, said on Wednesday in Addis Ababa that the bomb was thrown into Entasal hotel in the city of Gondar, late on Tuesday.
He also made known that three of the injured were in serious condition.
Tilahun said police were trying to track down the bombers, whose identity was not known, but who, he said, were likely to have been “anti-peace elements.”
Another bomb had exploded in Amhara capital, Bahir Dar, on January 4, but no injuries were reported.
Ethiopia has seen anti-government protests since November, 2015, mainly in the Oromia region, which includes Addis Ababa, and also in the Amhara region.
The Oromo ethnic group feels excluded from political and economic power, while the Amhara protests have focused on federal boundaries drawn two decades ago that are seen as cutting off many ethnic Amharas from the region.
The Amhara protests later turned to calls for wider political freedom and even for a change in government.
Ethiopia has arrested tens of thousands of people under a state of emergency that was declared in October, 2016.
The Ethiopian government later announced the release of nearly 10,000 of the people held.