Clashes broke out last week after months of tension between the government and the party that controls Tigray, the Tigray People’s Liberation Front (TPLF).
They both accuse each other of violating a 2022 peace deal that ended a brutal two-year civil war, which according to an Africa Union mediator is estimated to have cost 600,000 lives.
Last month, seven armed movements, including the TPLF and an Amhara militia known as Fano, formed an alliance with the stated aim of removing the government in Addis Ababa.
There is disagreement over which side started the latest fighting.
The TPLF says it was responding to a federal offensive, including drone strikes, while the government says Tigrayan forces attacked first after seizing control of airports in the region.
The BBC is unable to report from Tigray and surrounding areas.
It is difficult to verify what is happening on the ground and access to the internet and the main telecoms service provider in Tigray have also been cut.
Within Tigray, the national army and a pro-government militia appear to be advancing towards the region’s main city of Mekelle.
In the southern Tigrayan town of Alamata, a medic told the BBC on Wednesday that 52 civilians had died in three days of heavy fighting.
The TPLF is also reported to be fighting in neighbouring Afar region, a strategic area which connects landlocked Ethiopia to Djibouti and its ports.
A humanitarian source has estimated that tens of thousands have fled their homes in Afar, according to the AFP news agency.
Fighting around Lalibela in the Amhara region, a Unesco world heritage site where foreign tourists have been stranded for more than a week, has involved the national army and Fano fighters, now allied to the TPLF.
The government has accused neighbouring Eritrea of backing these groups.
One pro-government militia commander fighting in Tigray told the BBC that Eritrean soldiers were involved on the front lines.
