Malaysia Airlines has confirmed on Twitter that it has lost contact with Flight 17 which left Amsterdam and was heading to Kuala Lumpur.
The last known position of the Boeing 777-200 was over Ukrainian airspace and this video posted on Youtube looks like the aircraft may have crashed.
Early reports on Twitter suggest the airplane may have been shot down by a surface-to-air missle, but that information is still unconfirmed.
There were 295 passengers and crew on the aircraft. It's last known altitude, according to Flight Aware, was 33,000 feet at a speed of 562 miles per hour.