The Antonov-12, operated by a Ukraine-based company, was flying from Serbia to Jordan when it went down on Saturday close to the city of Kavala.
It was not immediately known whether there were any survivors.
Greece’s ERT state broadcaster reported that the aircraft had been carrying a 12-tonne cargo.
It has been described as potentially dangerous. On Sunday morning, emergency services were using a drone to survey the site of the wreckage out of caution. State-run TV reported the army, explosives experts and Greek Atomic Energy Commission staff would not approach until it was deemed safe.
“The (air) measurements at the moment have not shown anything but nonetheless instability in the field was observed,” Lieutenant General Marios Apostolidis, of the Northern Greece Fire Brigade, told reporters.
“In other words, intense smoke and heat, as well as a white substance that we do not recognise, so a special armed forces team has to inform us what it is and whether we can enter the field.”
The pilot had reportedly requested an emergency landing at Kavala airport due to an engine problem but was unable to reach the runway.
The plane was noticed at about 22:45 local time (19:45 GMT) by local residents. Footage appears to show it was already on fire as it descended.
Aimilia Tsaptanova – who saw the plane come down – said she was amazed it hadn’t crashed into their homes.
“It was full of smoke, it had a noise I can’t describe and it went over the mountain,” she said. “It passed the mountain and turned and crashed into the fields.