The Ukrainian government says the Malaysia Airlines flight was shot down.
The government in Kyiv and pro-Russia separatists fighting in Ukraine's eastern region both denied they were responsible for bringing down the plane.
Foreign Affairs Minister John Baird tweets that he was horrified to learn of the crash and that the government is following the situation closely.
The airline says it was notified by Ukrainian aviation authorities that they lost contact with flight MH17 about 50 kilometres from the border with Russia.
Ukrainian President Petro Poroshenko is calling for an international investigation into the crash, saying it was an act of terrorism.