According to accounts, an air raid targeting one of Myanmar’s largest ethnic insurgent groups killed at least 50 people and injured about 100 more.
Colonel Naw Bu, a spokesman for the Kachin Independence Army, provided the death toll to the BBC (KIA).
Witnesses in Kachin State, northern Myanmar, say three bombs were dropped on a KIA performance in Kansi village.
Villagers said there was no warning before the raid.
The concert in Kansi was to mark the 62nd anniversary of the rebel army’s campaign for autonomy.
Witnesses reported three huge explosions at around 20:30 (14:00 GMT) local time on Sunday. They ripped apart the cluster of buildings at the base and caused heavy casualties in the audience.
Among those killed are believed to be four popular Kachin singers. Eyewitnesses say the military blocked medics trying to move the injured to the nearby town of Hpakant, which has a hospital.
This part of Kachin State has been fiercely contested for many years by the military and Kachin insurgents because of its jade mines, which are thought to be worth around $30bn (£27bn) a year.
There has been frequent fighting there before and after the military coup last year, which deposed the civilian government led by Aung San Suu Kyi.
This attack may be retribution, or a warning, from the military, over the support the Kachin insurgents have been giving to other armed groups in Myanmar formed to resist the coup.