Dozens of bodies were scattered around the smouldering wreckage of a passenger jet that crashed in a field in eastern Ukraine on Thursday, a Reuters reporter said.
An emergency services rescue worker said at least 100 bodies had so far been found at the scene, near the village of Grabovo, and that debris from the wreckage was spread across an area up to about 15 km (nine miles) in diameter.
Broken pieces of the wings were marked with blue and red paint - the same colours as the emblem of the Malaysian airline which lost track of a Boeing 777 en route from Amsterdam to Kuala Lumpur that was carrying almost 300 people.
"I was working in the field on my tractor when I heard the sound of a plane and then a bang and shots. Then I saw the plane hit the ground and break in two. There was thick black smoke," said a witness, who gave his name only as Vladimir.
A separatist rebel from nearby Krasnyi Luch who gave his name only as Sergei said: "From my balcony I saw a plane begin to descend from a great height and then heard two explosions.
He denied the rebels had shot the plane down.
"This could happen only if it was a fighter jet or a surface-to-air missile (that shot it down)," he told Reuters, saying the rebels did not have weapons capable of shooting shoot down a plane at such a height.
All 295 people aboard the plane were killed, a Ukrainian interior ministry official said, blaming "terrorists" using a ground-to-air missile.
Ukraine's prime minister called the downing of the flight from Amsterdam to Kuala Lumpur a "catastrophe".
Separatist leader Aleksander Borodai blamed the downing of the passenger airliner on the country's government forces.
"Apparently, it's a passenger airliner indeed, truly shot down by the Ukrainian Air Force," Borodai told Russia's state-run Rossiya 24 TV broadcaster.
Malaysian Prime Minister Najib Razak he was "shocked" by the incident. "We are launching an immediate investigation," he said on his Twitter feed.
Russian President Vladimir Putin in a telephone conversation told U.S. President Barack Obama that a Malaysian airplane crashed on Ukrainian territory, the Kremlin said on Thursday.
The two leaders held a pre-planned call on the situation in Ukraine during which information became available from air traffic controllers about the crash.