Greece on Monday filed formal complaints to Serbia and Ukraine over the military cargo on a plane that crashed in its territory during an emergency landing, a Greek foreign ministry source said.

The Antonov An-12 aircraft, which crashed near the northern Greek city of Kavala late on Saturday evening killing all eight crew members onboard, was carrying 11.5 tonnes of Serbian-made mortar ammunition to Bangladesh, which was the buyer.

The plane was operated by the Ukrainian cargo carrier Meridian. The Ukrainian foreign ministry said the eight flight crew were Ukrainian citizens.

A Greek foreign ministry source on Monday said Athens had formally complained to Belgrade and Kiev over not being given prior warning on the nature of the cargo.

The official said Greece's ambassador in Belgrade had been instructed "to deliver immediately a complaint to Serbia stressing the need for the Greek authorities to be notified in advance about the nature of the cargo."

Hours later, the Ukrainian ambassador in Athens was delivered a similar complaint, the official said.

There was confusion initially over the plane's cargo and its final destination.

It took off from the Serbian city of Nis on Saturday and had been due to make a stopover in Amman, Jordan. 

Witnesses said they saw the Antonov on fire and heard explosions. Videos shared on social media showed the plane engulfed by a giant fireball as it hit the ground late Saturday.

Debris scattered across a wide area, and the crash site -- surrounded by fields -- was visible from the air, an AFP photographer said.

Explosives disposal experts were working for a second day on Monday to clear widespread ordnance at the site, so the area could be decontaminated and made accessible.

Locals have reported respiratory irritation in the aftermath of the crash.

The authorities have forbidden residents from entering nearby fields until the wreckage and any unexploded munitions have been removed.