Security forces opened fire in the Yangon area of Hlaing Tharyar as protesters used sticks and knives.
The junta declared martial law in the area after Chinese businesses were attacked. Protesters believe China is giving support to the Burmese military.
Myanmar has been gripped by protests since the military coup on 1 February.
Military rulers have detained Aung San Suu Kyi, the country's civilian leader and head of the National League for Democracy (NLD) party.
The NLD won a landslide in last year's election but the military alleged there had been widespread fraud.
Some of the ousted MPs have refused to accept last month's coup and have gone into hiding.
In his first public address, their leader Mahn Win Khaing Than urged protesters to defend themselves against the military crackdown during what he called a "revolution".
"This is the darkest moment of the nation and the moment that the dawn is close," he said.
In addition to those killed in Yangon on Sunday, further deaths and injuries were reported elsewhere in the country.
The Assistance Association for Political Prisoners (AAPP) monitoring group put the day's death toll at 38.