Anton Gerashchenko, an adviser to Ukraine's interior minister, has written on Facebook (Russian) that "280 passengers and 15 members have died" in the crash, and that the plane was last recorded flying at 10,000 meters.
He links to an unverified video showing smoke rising in eastern Ukraine, and accuses militants of shooting down the plane: "A civilian airliner travelling from Amsterdam to Kuala Lumpur has just been shot down by a Buk anti-aircraft system.