An AFP reporter said there was a massive crater at the crash site, with belongings and airplane parts scattered widely.
The Max mock-up is the newest version of Boeing's workhorse 737 models, the world's most popular commercial aircraft.
The Swedish-based flight tracking organisation said on its Twitter feed: "Data from Flightradar24 ADS-B network show that vertical speed was unstable after take off".
Safety experts cautioned against drawing too many comparisons between the two crashes until more is known about Sunday's disaster.
They said investigators would examine the wreckage and bodies for any signs of burns or unusual forces and study the shape and size of the wreckage field.
Investigators say that the pilots of the 737 Max-8 aircraft have been struggling with a new feature of the aircraft, which is an automated system created to keep the plane from stalling. Southwest Airlines flies 31 MAX 8 jets while American Airlines and Air Canada each have 24 in their fleet.
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The plane crashed six minutes after departing, plowing into the ground at Hejere near Bishoftu, or Debre Zeit, some 50 kilometers (31 miles) south of Addis Ababa, at 8:44 a.m. The Ethiopian Airlines plane was "brand new" and had been delivered to the airline in November, GebreMariam said.
The crash was similar to that of a Lion Air jet of the same model in Indonesian seas previous year, killing 189 people.
Ethiopian officials declared Monday a day of mourning.
In the USA, the Federal Aviation Administration said it would join the National Transportation Safety Board in assisting Ethiopian authorities with the crash investigation. The decision was made before US investigators reached the crash site, the Journal said.
The plane, which crashed shortly after takeoff from Addis Ababa, had 149 passengers and eight crew members on board, the airline said. It has flown more than 1,200 hours.
Ethiopian Prime Minister Abiy Ahmed tweeted confirming deaths but did not give a number.
Airlines in Ethiopia, China, Indonesia and elsewhere grounded the Boeing 737 Max 8 jetliner Monday after the second devastating crash of one of the planes in five months.