The MNDAA had observed a ceasefire with the Myanmar government since 1989.
Commenting on the government's moves in Myanmar, Aung Zaw, editor of the Irrawaddy magazine, told Al Jazeera: "[Action] is being taken against the Wa Chinese minority who are living in the Kokang area."
The Wa are one of China's more than 50 ethnic groups, and have a population of around 400,000 in China alone, with more living in Myanmar.
"The situation remains tense," Aung Zaw said. "I've been told around 2,000 Wa soldiers [militia members] are stationed in Kokang. At the same time, the Burmese [forces] are requesting more reinforcements.
"Chinese authorities told me that if the two sides could not resolve the situation in the next two days, it could lead to a full-blown conflict."
On Friday, one person was killed and several people were injured by a bomb thrown across the Chinese border, He Yongchun, a senior official from China's Red Cross, told the China Daily.
Hospital officials in Nansan confirmed that injured people had been treated in hospitals there.
China has called on Myanmar to maintain stability in the border region and urged more measures to protect the security and legal rights of Chinese citizens there.
Covering an area of over 10,000sq km, the Kokang region bordering China's Yunnan province has a population of about 150,000 people.
It is home to a large number of ethnic Chinese, many of whom are Chinese citizens who own businesses in Myanmar.
Kitty McKinsey, a UNHCR regional spokesman, told Al Jazeera: "The Chinese in Yunnan have given the tens of thousands of refugees crossing into China aid and medical care. About 30,000 have crossed over.
"These people seem to have appeared from nowhere. UNHCR is not on the ground in Kokang, we don't operate there. I do believe this [turn of events] took a lot of people by surprise."
The refugees included Myanmar citizens and some Chinese businesspeople, Yu Chunyan, press officer of Yunnan Foreign Affairs Office, said.
Thousands more people are trapped in Kokang, where there are now food and water shortages, the Global Times reported.
A Chinese shopkeeper who fled the area said on Friday that some merchants who stayed beyond to protect their property had been killed.
Security forces have been beefed up along the border region, a lush, forested area of low hills, to prevent the conflict from spilling into Yunnan.