Ukraine says a plane carrying 295 people was shot down as it flew over the country.
Both the government and the pro-Russia separatists who have been fighting in the region denied any responsibility for downing the plane.
The plane was a Malaysia Airlines Boeing 777, flying from Amsterdam to Kuala Lumpur.
It crashed in the village of Grabovo, in eastern Ukraine.
That village is controlled by separatists, who want the region to join Russia.
Malaysia's prime minister says his country is launching an immediate investigation.