The organisation denounced arbitrary arrests, detentions and torture of civilians by the military "based solely on ethnicity" and said that the soldiers also "fired indiscriminately in civilian areas," forcing thousands to flee their homes.

"The Myanmar military is as relentless and ruthless as ever, committing war crimes against civilians in northern Shan State with absolute impunity," Amnesty's Director for east and southeast Asia, Nicholas Bequelin, said in statement.

According to Amnesty, the military's 99th Light Infantry Division is behind much of the violence - the same division involved in the 2017 offensive and atrocities against the Rohingya Muslim minority.

The civilian population also suffer abuses by ethnic armed groups, who abduct, detain and sometimes torture them, subject them to forced labour and extort food and money from them, Amnesty said.

Fighting in the north of Shan state intensified in mid-August as peace negotiations between the government and some 20 rebel groups have been deadlocked for more than a year.

Ethnci minorities in Myanmar, which include the Shan, Karen, Rakhine, Mon, Chin, Kayah and Kachin, represent more than 30 per cent of the 53 million population.

Australian Associated Press