Thousands of people are feared to have been displaced by four days of fighting in northern Myanmar, including several hundred who reportedly fled to China, the United Nations said Monday.

On Friday, three powerful ethnic armed organizations attacked junta troops across a swathe of northern Shan state, home to a planned billion-dollar rail link, part of Beijing's Belt and Road infrastructure initiative.

The Ta'ang National Liberation Army, the Arakan Army and the Myanmar National Democratic Alliance Army have since said they have seized several military posts and key roads.